Friday, January 30, 2009

What are the Breeding Methods in Plants

Breeding Methods in Plants:

Breeding plants to create new varieties and improve upon old ones is a hobby that nearly everyone can engage in. The crossing techniques are easy to learn and breeders can experiment with many kinds of plants. Generally, amateur plant breeders work with traits that are fairly easy to change-for example, flower color, fruit shape, or plant size. Nevertheless, although experiments may be simple, it is possible to produce unusual or beautiful plants. In order to breed plants successfully it is important to understand the principles of plant reproduction. The purpose of this is to explain the simple techniques that can be used to produce new varieties or strains of plants.

The first step in the plant hybridization procedure is the selection of parent plants with the desired characteristics. Plant characteristics can be changed after many generations by a process of selection. There are two types of selection-natural and artificial. Natural selection is the process that occurs in nature whereby strong and well-adapted plants survive while weak and poorly adapted plants eventually die out. This process has taken place since the beginning of life on earth and it is still occurring in nature. Artificial selection is the process that humans use to obtain more desirable types of plants. Thousands of years ago people learned that saving seed from the kind of plant they wanted to continue growing would increase the chances of getting a plant similar to the original. But our ancestors didn't know what their chances of success were nor did they understand the processes by which traits were changed or maintained. It wasn't until the eighteenth and nineteenth centuries that humans began to understand the laws of heredity and the processes of plant reproduction. Even today, these fundamentals aren't completely understood. But enough is known so that we can select plants for breeding with considerably more assurance of success than our ancestors did.

In our experiment we have to select the parents for the process of hybridization. The plants selected for breeding should be sturdy and healthy. It is usually easier to tell which ones are healthy after a few flowers on the plant have bloomed. Some plants have natural barriers to cross- or self-pollination. It is advisable to check for this before breeding, for although barriers can be overcome, some plants cannot be artificially pollinated. An example of a barrier that cannot be overcome is the selfpollination prohibitor of some orchids; the stigmas of certain orchids produce a substance, which kills the pollen of flowers of the same plant. The mechanism that performs this cannot be removed without destroying the pistil. In choosing a pollen parent (male parent), select one that has a heavy yellow powder on the anther. This powder is the pollen. In choosing a seed parent, examine the stigma. It should have either a glistening substance on it that is sticky to the touch or a "hairy" surface. It is this substance or surface that retains the pollen, thus making fertilization possible. Once the seed parents and pollen have been selected, you are ready to begin pollination.

Tags: Bio Technology, Bio Genetics, Breeding Methods in Plants

How to practically do Conjugation of Bacteria

Here practical steps are being described to perform conjugation of Bacteria.

Take two strains of bacterial cultures of e.coli. One is the male strain or the P+, which is auxotrophic for biotin and methionine (Bio-, MeC). This bacterium can grow in the minimal medium, only if these two components are supplemented. Similarly, the female bacteria or the P- strain is able to produce both biotin and methionine, but are auxotrophic for threonine and leucine (Thr-, Leu-). These bacteria cannot grow in the minimal medium unless the respective nutrients are supplemented.

But when these two populations are mixed and grown in media with only the salts and the carbon source (minimal media) some of the cells could grow without the supplementation of the additional amino acids and vitamin, biotin. This indicates that when grown together some female cells receive the functional genes of Thr and Leu from the male strains by conjugation. Similarly, some of the male strains receive the functional genes for biotin and methionine from the female strain. These new genetically transformed strains can grow in the minimal medium without any additional nutrient supplementation.

This is a common method of natural recombination in bacteria resulting in the formations of variants. In this context it is very important because conjugation can produce drug resistance among pathogenic bacteria. Therefore, the mechanism of conjugation has to be clearly understood and should be aware that in heterogonous cultures there is the chance of bacterial conjugations and genetic recombinations resulting in new strains with new weapons. Contaminated laboratory cultures, organic factory effluents, and sewage water are good media for bacterial conjugations.

Tags: Bio Technology, Bio Genetics, Bacterial Conjugation

How to practically carry out Bacterial Transformation

Bacterial transformation is routine work in all molecular biology laboratories as part of recombinant DNA experiment or gene cloning. In rDNA experiments or gene cloning, we prepare recombinant DNA or the gene or plasmid to be cloned, which has to be transferred to a host cell so that the DNA will multiply inside the bacterial cell. Transfer of the plasmid or the rDNA is carried out by bacterial transformation.

The first step is to select a suitable host cell such as a suitable strain of e.coli like DH5 a , a common strain available in all molecular biology laboratories, which can take foreign DNA easily. For this we have to treat the grown bacterial cultures at its log phase of growth, with CaCl2. Centrifuge the cells growing at the log phase under low rpm (3,000-5,000 for 10 minutes) at 4°C and collect the cells. Suspend the cells in chilled CaCl2 of 0.1 M. The cells in calcium chloride are able to accept the small DNA molecules. These cells in CaCl2 can be stored for a long time under low temperatures such as -20 or -70°C.

Sudden exposure of this cell to the room temperature or higher can force the cell to take the DNA from outside. Take the stored competent cells, which are in the frozen condition and add the DNA sample to these cells and expose them to a higher temperature, at 42°C for two to three minutes. Some of these cells take the DNA from outside and will be transformed by intercalating with its genome. These cultures can be plated on a selection agar plate and the transformed colonies can be selected against the untransformed ones.

This transformation is extensively used in genetic engineering experiments. Any gene or DNA, before transferring into an organism, can be tested in a selected host by this transformation method. New promoters can be checked for their strength of expression. Commercially-useful enzymes and therapeutic proteins can be prepared in industrial scales. In short, any genetic engineering or gene cloning cannot be accomplished without bacterial transformation.

Tags: Bio Technology, Bio Genetics, Bacterial Transformation

Artificial alteration of Genes in Bacteria through Recombinant DNA Technology

Genes in bacteria can also be altered artificially through recombinant DNA technology.

In recombinant DNA technology, endonucleases and ligase enzymes are routinely employed. Restriction endonuclease enzymes are naturally occurring enzymes in bacteria that help protect bacteria from viral attacks by cutting up the foreign viral DNA while not harming the bacterium's own DNA. Restriction endonuclease enzymes recognize specific palindromic deoxyribonucleotide base sequences (base sequences that read the same forward and backward on the complementary DNA strands), and then split each DNA strand at a specific site within that sequence.

For example, escherichia coli makes a restriction endonuclease called eco R1 that recognizes the deoxyribonucleotide base sequence G-A-A-T-T-C and cuts the DNA strand between the G and the A. Since the complementary strand has the sequence CTTAAG, it is also cut between the G and the A. This leaves short, complementary, single-stranded sticky ends capable of hydrogen bonding with the complementary sticky ends of DNA fragments cut by the same enzyme.

Tags: Bio Technology, Bio Genetics, Artificial alteration of Genes

Types of Bacterial Conjugation

Bacterial conjugation is of following types

F+ conjugation:
This results in the transfer of an F+ plasmid (coding only for a sex pilus) but not chromosomal DNA from a male donor bacterium to a female recipient bacterium. One plasmid strand enters the recipient bacterium while one strand remains in the donor. Each strand then makes a complementary copy. The recipient then becomes an F+ male and can make a sex pilus. Other plasmids present in the cytoplasm of the bacterium, such as those coding for antibiotic resistance, may also be transferred during this process.

Hfr (high-frequency recombinant) conjugation:
An F+ plasmid inserts or integrates into the nucleoid to form an Hfr male. The nucleoid then breaks in the middle of the inserted P plasmid and one DNA strand begins to enter the recipient bacterium. The bacterial connection usually breaks before the transfer of the entire chromosome is completed so the remainder of the F+ plasmid seldom enters the recipient. As a result, there is a transfer of some chromosomal DNA, that may be exchanged for a piece of the recipient's DNA, but not maleness.

Resistance plasmid conjugation:
This results in the transfer of a resistance plasmid (R-plasmid) from a donor bacterium to a recipient. One plasmid strand enters the recipient bacterium while one strand remains in the donor. Each strand then makes a complementary copy. The R-plasmid has genes coded for multiple antibiotic resistance and sex-pilus formation. The recipient becomes antibiotic resistant and male and is now able to transfer R-plasmids to other bacteria.

Tags: Bio Technology, Bio Genetix, Bacterial Conjugation

Monday, January 26, 2009

Various Mechanisms of Genetic Recombination

Genetic recombination is the transfer of DNA from one organism to another. The transferred donor DNA may then be integrated into the recipient's nucleoid by various mechanisms.

Mechanisms of genetic recombination include:

1) Transformation: DNA fragments (usually about 20 genes long) from a dead degraded bacterium bind to DNA-binding proteins on the surface of a competent recipient bacterium. Nuclease enzymes then cut the bound DNA into fragments. One strand is destroyed and the other penetrates the recipient bacterium. This DNA fragment from the donor is then exchanged for a piece of the recipient's DNA by means of Rec A proteins.

2) Transduction: Transfer of fragments of DNA from one bacterium to another bacterium by a bacteriophage.

(a) Generalized transduction: During the replication of a lytic phage, the capsid sometimes assembles around a small fragment of bacterial DNA. When this phage infects another bacterium, it injects the fragment of donor bacterial DNA into the recipient where it can be exchanged for a piece of the recipient's DNA. Plasmids, such as the penicillinase plasmid of Staphylococcus aureus, may also be carried in a similar manner.

(b) Specialized transduction: This may occur occasionally during the lysogenic life cycle of a temperate bacteriophage. During spontaneous induction, a small piece of bacterial DNA may sometimes be exchanged for a piece of phage genome (that remains in the nucleoid). This piece of bacterial DNA replicates as a part of the phage genome and is put into each phage capsid. The phages are released, adsorbed into recipient bacteria, and injected into the donor bacterium DNA/phage DNA complex and into the recipient bacterium where it inserts into its nucleoid.

3) Bacterial conjugation: Transfer of DNA from a living donor bacterium to a recipient bacterium. In gram-negative bacteria, a sex pilus produced by the donor bacterium binds to the recipient. The sex pilus then retracts, bringing the two bacteria into contact. In gram-positive bacteria sticky surface molecules are produced that bring the two bacteria into contact. DNA is then transferred from the donor to the recipient.

Tags: Bio Technology, Bio Genetics, Genetic Recombination

Understanding of Mutagenic Techniques

Mutations are heritable changes that occur in the genome or DNA. Normally, these changes are harmful to the organism, a small percentage of mutations are useful in the process of evolution. Mutations can be induced with the help of different mutagenic agents and chemical or physical methods to create improved qualities in microbial systems and in plants for producing improved crop varieties. For example, improved agronomic characteristics such as disease resistance, salt tolerance, early flowering, pest resistance, early maturing, grain size, etc.

Bacterial Mutagenesis: The best-suited method for inducing mutation in microbes such as bacteria is radiation, particularly UV-radiation.

The following is an experiment to induce mutation in bacteria with UV-radiation:

Step –1: Make a bacterial culture by inoculating a bacterial colony (s strain of e.coli) to a small volume of broth culture (liquid medium; LB medium or the minimal medium) and grow the culture overnight in an incubator shaker at 37°C.

Step –2: The next day, spread 0.1 ml of overnight culture on LB agar plates using a bent 'L' shaped glass rod (spreader) that has been flamed after being dipped in alcohol. Each plate should be labeled properly to avoid confusion before starting the experiment.

Step –3: Now keep the agar plate containing the bacteria to be mutagenized under the UV lamp in a laminar flow chamber or hood. Remove the cover from the plate and close the door of the hood. Turn the UV lamp on and note the time of exposure of the bacteria to the UV light. (Exposure should be timed in seconds. You can find out the optimal time of exposure by repeating the experiment between 5 and 240 seconds to determine what is optimal.)

The UV lamp is very strong. Do not expose your skin to the UV light. Do not operate the UV lamp with the hood open. UV light can cause serious and permanent damage to your eyes. The glass in the hood door will absorb the UV light. Never look at the UV lamp when it is on without wearing eye protection. At the end of the time turn the lamp off.

Step –4: Replace the cover on the plate, remove it from the UV box, and place it in a 37°C incubator. Plates should be incubated upside down. This is important to prevent accumulation of condensation of moisture on the surface of the agar.

Step –5: 'Check plates after 24 hours and count or estimate the number of colonies on the plate, and check for the type of mutant that you are looking for.

Depending on the type of mutant that you are looking for, prepare another set of the agar media plates to grow and select the mutants. If your aim is to get an auxotrophic mutant for Arginine (Arg-), you prepare agar media plates with minimal media, which contains only the essential components in the form of salts and elements and no organic components except the carbon source in the form of glucose. Now transfer the colonies from the master plates to the selection plate by replica plating. Take a circular filter paper that fits inside the petriplate and gently keep it over the colonies on the master plate. Slowly take the filter paper and put it in the selection media and allow growing overnight inside the incubator. By comparing the colonies in the selection media with that of the master plate, you can find out the colonies on the master plate, which cannot grow on the minimal media. This can be confirmed by monitoring the growth of the colonies again on the minimal media, which is supplemented with arginine (arg + plates).

Seed Mutagenesis: In the case of agricultural plants seeds are the parts that can be used for inducing mutations. We can use both chemical as well as physical mutagens for creating mutations.

For this experiment, we can use a mutagenic chemical-EMS (ethyl methanesulphonate) for inducing mutations in wheat or any other experimental plants such as arabidopsis. Take a specific number of healthy seeds and soak them in water overnight. The next day, the water is blotted off with tissue paper or filter paper. Incubate the seeds in an aqueous solution of EMS of suitable concentration for about 2 hours at room temperature. Incubate some seeds in water under similar physical conditions and use them as the control for the experiment. Note the concentration and the time of treatment of the experiment. After the exposure, take the seeds out and wash them thoroughly with water to remove the traces of the mutagen. The treated seeds have to be sown in the controlled environment along with the control separately. After germination, the seedlings of the treated seeds can be compared with that of the control to evaluate the desired mutations.

The experiment can be repeated with different strengths (concentration) of the mutagens and time of exposure.

Tags: Bio Technology, Bio Genetics, Mutagenic Techniques

What are the various Applications of Chromosome Painting

Following are some of the applications of Chromosome Painting

1) To find out the location of a specific gene located on a specific chromosome: FISH hybridization is done with the appropriate gene-specific probe labeled with the fluorescent dye. The test will give the binding of the gene-specific probe labeled with the fluorescent dye to the respective chromosome at the specific position, where the gene is located.

2) Detection of translocation: Chromosomes that have undergone translocation will have two segments. When it is subjected to the technique of chromosome painting it will take different probes and appear in two colors or multicolored depending on the number of translocations.

3) Detecting chromosome abnormalities: FISH has improved the efficiency of screening cells for chromosome abnormalities in mutagenic studies and for testing the mutagenic ability of chemicals and other potent mutagens in the environment. It has also improved the detection of chromosome aberrations and rearrangements associated with tumour and cancer.

4) To find out the chromosomal similarity between divergent species: Use of the same chromosome paint for chromosomes of different species reveals the extent of chromosome rearrangements since divergence of the species. Such studies reveal extensive synteny between fairly divergent species.

5) Clinical applications: With the use of this technique, it is possible to easily identify the presence of numerous chromosomal translocations and unambiguously identify structural alterations in cancer cell lines (for example, a giant marker chromosome (marl) in the aneuploid breast cancer cell line, SKBR3). The application of these techniques should facilitate analysis of chromosomal aberrations and genetic abnormalities in various human diseases including cancer.

Tags: Bio Technology, Bio Genetics, Chromosome Painting

Chromosomal analysis by Chromosome Painting

Chromosome painting is a powerful tool for chromosomal analysis. The technique of labeling chromosomes with different colored dyes is known as chromosome painting. This is carried out by the technique known as FISH or Fluorescent In Situ Hybridization.

FISH has been used to detect the location of specific genomic targets using probes that are labeled with specific fluorochromes. The technique allows detection of simple and complex chromosomal rearrangements. In addition, complex chromosomal abnormalities can be identified that could not be detected by the conventional cytogenetic banding techniques.

In the July 26,1996 issue of Science, Schrock, et al. reported the development of a similar technique that allows the multi-color detection of human chromosomes. The technique is known as Multiplex-fluorescence In Situ Hybridization (M-FISH). The technique has been accomplished by allowing 24 combinatorially labeled chromosome-painting probes to hybridize with human chromosomes. Then, the emitted spectrally overlapping chromosome specific DNA probes are resolved using computer separation (classification) of the spectra.

This technique can be used for detection of chromosomal abnormalities. On the basis of the location of the probes used, the size of the alteration can be estimated. In addition, the developed technique provides information that complements conventional banding analysis. With the use of this technique, it is easy to identify the presence of numerous chromosomal translocations and unambiguously identify structural alterations including a giant marker chromosome (marl) in the aneuploid breast cancer cell line, SKBR3. The application of these techniques should facilitate analysis of chromosomal aberrations and genetic abnormalities in various human diseases including cancer. These new techniques will undoubtedly find wide clinical applications, and specifically the characterization of complex karyotypes will complement standard cytogenetic studies.

The basic steps in the technique of chromosome painting are:

a) Collection of nucleic-acid sequences specific for each of the individual chromosomes. These sequences should not be present in other chromosomes.

b) The sequences specific for each chromosome are converted into probes by labeling them with fluorescent dyes. Probes for each chromosome should be labeled with different (colors) fluorescent dyes.

c) In situ hybridization of each probe with the target chromosomes within the cells. Simultaneous hybridization with all probe set results in a chromosome spread preparation, in which each of the set of homologous chromosomes appears a different color when viewed with a fluorescent microscope.

Tags: Bio Technology, Bio Genetics, Chromosomal Techniques

Know the process of Karyotyping

Karyotyping is a valuable research tool used to determine the chromosome complement within somatic or cultured cells. It is important to keep in mind that karyotypes evolve with organisms. Because of this evolution, it is important for the interpretation of biochemical or other data, that the karyotype of a specific subline be determined. Many morphological and physiological problems can be traced to the change in the karyotype. Numerous technical procedures have been reported that produce banding patterns on metaphase chromosomes. A band is defined as that part of a chromosome, which is clearly distinguishable from its adjacent segments by appearing darker or lighter. The chromosomes are visualized as consisting of a continuous series of light and dark bands. A G-staining method resulting in G-bands uses a Giemsa dye mixture or Leishman dye mixture as the staining agent.

Karyotypes are usually prepared from cells in which chromosomes can be readily distinguished, counted, and measured. Chromosomes at the mitotic metaphase, meiotic metaphase II, and pachytene of meiosis are best suited to make and evaluate the karyotypes. After taking the microphotograph of the complete chromosomes, a photograph karyotype may be prepared by cutting out the chromosomes from the microphotograph and arranging them in ordered pairs. A diagrammatic representation of karyotype is called an idiogram. It can be prepared by taking measurements and drawing the chromosomes with all their relative differences. An idiogram represents the diploid complement of chromosomes. It shows the number, size, and shape and allows easy comparison of chromosomes within the karyotype and also with other organisms.

The position of the centromere with respect to the length of arms is called arm ratio of the chromosomes.

Karyotyping is often used for the parental diagnosis and detection of variations in the chromosome number and structure, aberrations, and anomalies, which are the common cause of many congenital defects and spontaneous abortions.

Tags: Bio Technology, Bio Genetics, Karyotyping

Types of Chromosomal Banding Patterns

Most of chromosomes, at the prophase and the metaphase, are characterized by a banding pattern. But this banding pattern is more evident and clear in the case of larger chromosomes such as the polytene chromosomes of drosophila melanogaster, or the fruit fly. The banding patterns are the regions rich in heterochromatin, where the histone-DNA interaction is more. These complexes can be stained very easily by the conventional nuclear dyes or chromosomal dyes such as orcein. The regions between the bands are actually the active regions of the chromatin where more genes are present, but the quantity of DNA is very low and therefore the histone proteins. That is why they appear unstained or colored lightly. These interband regions can be detected with immuno-staining by using fluorescently labeled antibodies against the DNA-dependent RNA polymerase, which is usually seen with euchromatin regions required for the process of transcription.

Specialized staining techniques are now available, which enable one to differentiate or precisely identify individual chromosome homologes, chromosome regions, and/ or chromosome bands. A renewed interest in the chromosomal or cytogenetic status of various species has been generated by the advancements of genetic mapping techniques utilizing fluorescence in situ hybridization or FISH. Depending upon the type of dye or fluorochrome or the chromosome pretreatment, there can be different types of banding patterns. They include banding patterns such as G-banding, Q-banding, C-banding, and R-banding. The data generated by multiple chromosome banding techniques can be used for karyotypic analysis.

Q-banding: This banding pattern is obtained by treating with a fluorochrome or the fluorescent dye quinacrin. They can be identified by a yellow fluorescence of different intensity. Most parts of the stained DNA are heterochromatin. Quinacrin binds those regions which are rich in AT and G-C, but fluorescences only A-T-quinacrin regions. A-T regions are seen more in heterochromatin than in euchromatin. Therefore, by this banding method heterochromatin regions are labeled preferentially. The characters of the banding regions and the specificity of the fluorochrome are not exclusively dependent on their affinity to regions rich in A- T, but it depends on the distribution of A- T and its association with other molecules such as histone proteins.

G-banding: This technique is not a fluorochrome-based pretreatment. It is well suited L "lr animal cells. It resembles the C-banding technique without pretreatrne.1.t. During mitosis, the 23 pairs of human chromosomes condense and are visible with a light microscope. A karyotype analysis usually involves blocking cells in mitosis and staining the condensed chromosomes with Giemsa dye. The dye stains regions of chromosomes that are rich in the base pairs Adenine (A) and Thymine (T) producing a dark band. A common misconception is that bands represent single genes, but in fact the thinnest bands contain over a million base pairs and potentially hundreds of genes. For example, the size of one small band is about equal to the entire genetic information for one bacterium.

C-banding: The name C-banding originated from centromeric or constitutive heterochromatin. The centromere appears as a stained band compared to other regions. The technique involves a pretreatment with alkali before staining. The alkaline pretreatment leads to the complete depurination of the DNA. The remaining DNA is again renatured and stained with Giemsa solution consisting of methylene azure, methylene violet, methylene blue, and eosin. In this staining the heterochromatin take a lot of stain but the rest of the chromosomes stain only a little. This banding technique is well suited for the characterization of plant chromosomes.

R-banding: This is known as a reverse banding technique. This technique results in the staining of areas rich in G-C that is typical for euchromatins. G-, Q-, and R-bandings are not observed with plant chromosomes.

Hy-banding: This is a common technique used with plant cells. The technique involves a pretreatment of the cells in which the cells are warmed in the presence of HCl and then stained with acetocarmine. The pattern of Hy-band is different from that of C-bands. The binding of histone protein to DNA and its complete extraction has an impact on the binding ability of acetocarmine and formation of bands.

Further variations in the procedure of the pre-treatment choice of dyes and fluorochromes further enhanced the resolution of the banding techniques. Many of the techniques are well suited for animal chromosomes, but face many difficulties with plant chromosomes. The reason for this is not well understood. The banding pattern of plant chromosomes with any of these techniques never comes to the same degree as that of animal chromosome banding patterns. The consistent banding patterns of the constitutive heterochromatin and the remaining chromatin are exactly constant in many species with an intraspecific variable karyotype.

Tags: Bio Technology, Bio Genetics, Chromosomal Banding

What are the Chromosomal Techniques

Cytological studies of chromosomes actually started in 1956 when Joe Bin Tjio and Albert Levan used a hypotonic solution to break open the cell and release the chromosomes. They showed for the first time that the human chromosome number is 46 (2n = 46). Following this, chromosomal techniques were developed to study the chromosomal basis of inheritance and the relationship between genetic syndromes and chromosomal aberrations. In 1959, it was shown that Down's Syndrome is due to an additional chromosome (2n + 1 = 47). Later, it was identified as chromosome number 21. New methods and staining techniques have been developed to produce well-spread preparations of human chromosomes.

Human mitotic chromosomes can be prepared from lymphocytes by arresting the cell division at the metaphase using the chemical colchicine. Then the chromosomes can be released by treating the cells with a hypotonic solution. Various staining techniques can be used to view the chromosomes. In the beginning, identification of chromosomes was based on the position of the centromere and length of the chromosomes. But at present time there are a number of other selective staining and banding techniques used to identify certain specific regions of the chromosome, which include labeling of the chromosomes with fluorescent dyes or radiolabeled compounds. Another powerful technique of modem times is the in situ hybridization of specific chromosomes with radiolabeled or fluorescently labeled nucleic acid probes to locate the position of specific genes. The following are some of the routinely used chromosomal techniques. The same types of techniques were conducted with plant cells also, with root tips and flower buds mainly to study about the behavior of chromosomes during mitosis and meiosis; and also to study about polyploids and other types of chromosomal aberrations.

Staining Techniques for Nucleic Acids
Since nucleic acids are an essential component of chromosomes, certain nucleic acid-staining techniques can be used for the detection of chromosomes and their specific areas. There are mainly three staining techniques that can be used for the visualization of chromosomes.

1) Histochemical stains: These stains selectively bind to certain cellular parts or components depending on their chemical nature.

2) Stains based on antibodies: Stains based on antibodies, which are highly selective in their binding. They are able to bind specific gene sequences very specifically. The nucleic acid parts or chromosome parts can be visualized if the antibodies are fluorescently labeled. This type of staining is known as immuno-staining.

3) Radiolabeled stains: This staining technique can be used for visualizing the nucleic acids within the nucleus. Here, we use radiolabeled nucleotides (labeled with 3H; for example, 3H labeled uridine, which may be used specifically to detect and quantify RNA content). This is another technique of in vivo labeling. Radiolabeling has to be coupled with autoradiography for visualization or detection.

Tags: Bio Technology, Bio Genetics, Chromosomal Techniques

Wednesday, January 21, 2009

Know all about Defense Mechanisms in Microbes and Insects

Defense Mechanisms in Microbes and Insects :
It was once believed that lower organisms do not have defense mechanisms. But this is not true. Even though a well-developed defense mechanism is present only in vertebrates, simple forms of defense mechanisms and immune systems are also available in lower forms of organisms. In vertebrates, as we move down from mammals to birds, to reptiles, to amphibians and to fish, the immune system becomes simpler. Lower organisms do not have a well-established defense mechanism or immune system as we have discussed in the case of vertebrates, but these organisms can also protect themselves from enemies and competitors by other types of defense mechanisms, some of, which are specific for a particular organism.

Defense mechanism in Microbes :
Bacteria and other microorganisms have various types of structural and physiological or biochemical means for defense against their enemies and adverse situations. A large number of bacteria and fungi produce digestive enzymes and toxic chemicals such as antibiotics and antimicrobial compounds. These compounds can kill or damage the cells of organisms in which they are in contact.

Many bacteria and other microorganisms are capable of producing capsules.

The phagocytic cells cannot engulf and destroy the capsulated bacterial cells. Phagocytes such as macrophages and neutrophils can easily engulf the noncapsulated bacterial cells and destroy them easily.

During unfavorable conditions, a large number of bacteria can be changed into spores, known as endospores. The cytoplasm of the cell is detached from the cell wall and changed into a spore in the middle of the cell. The spore has a very thick covering, and since it is formed within the cell, it is called an endospore. Endospores are highly resistant to heat, UV-radiations, and chemicals and antibiotics. Even though the formations of endospores are a mechanism to overcome the unfavorable conditions, the formation of such endospores can be considered a defense mechanism.

Defense mechanism in Insects :
There are different types of defense mechanisms in insects, which depends on the species of the insect. One of the main mechanisms is the production of antibacterial peptides. These toxic compounds are capable of killing bacteria. A large number of other insects also produce these types of toxic antibacterial peptides and are called cecropins. Bees produce a type of toxin called melittin, which is present in their venom and are able to do the hemolytic activity (lysing the RBC). In insects like the fruit fly (drosophila) the reproductive organs produce antibacterial peptides, the andropins. In certain other insects antibacterial pep tides are present in the hemolymph. Some of these antibacterial pep tides are produced in response to the bacterial infection in insects. In addition to these defense mechanisms, they also possess phagocytic cells. These cells can attack and destroy the invading microorganisms and pathogens.

Tags: Bio Technology, Bio Genetics, Defense Mechanisms

Utility of Secondary Metabolites

Secondary Metabolism:

Biomolecules such as amino acids, lipids and carbohydrates such as glucose, fatty acids, etc. are involved in the synthesis of various macromolecules such as proteins, nucleic acids, starch and lipids such as triglycerides, steroids, etc. These types of molecules and other related activities such as generation of energy, immunological activities, etc., are essential for the existence of life activities. Such reactions are known as primary metabolism and their products are called primary metabolites. But organisms, when they become mature or when the cells come to the lag phase of growth, operate additional metabolic pathways to synthesize certain compounds, which are not essential for carrying out normal life activities. Such compounds are known as secondary metabolites and their biosynthetic pathway is known as secondary metabolism. Their biosynthesis starts from some primary metabolite or from intermediates of the primary metabolism.

These secondary metabolites are produced in small quantities and are believed not to have any function in the body. But it has been observed that in some cases they have some role in the defense against microorganisms or insects and pests. Even some secondary metabolites are produced in response to the attack of some microorganisms or insects. Some compounds impart special odors to body parts such as flowers or leaves, which attracts or keeps away insects and predators. In plants, there are various types of secondary metabolites such as alkaloids, steroids, terpenes, latex, tannins, resins etc., which are produced and stored in specialized cells, in most cases.

In the case of bacteria and fungus these secondary metabolites are produced at the stationary phase of the growth. Compounds such as antibiotics are the secondary metabolites accumulated by the bacterial cultures and fungus at their stationary phase of growth. The biosynthesis of secondary metabolism is dependent on the state of growth and growth conditions. It is possible to alter the sequence of secondary metabolism by altering growth conditions and media compositions, in the case of bacteria and fungi. Even a change in the pH can alter the route of secondary metabolism in microbial cultures.

Secondary metabolites such as alkaloids, latex, and antibiotics are of great economic value for man. Therefore, these compounds can be synthesized in large quantities by manipulating culture conditions, or by adding the necessary precursors in the media of the cultures.

Tag: Bio Technology, Bio Genetics

Tuesday, January 20, 2009

Know all about Plant-Pathogen Interaction

When an insect or microbe attacks a plant it triggers a chain of reactions leading to the production of some compounds that can act against the invading organisms. This process is called elicitation and the compounds produced in responds to the insect or microbial attack are called phytoalexins.

Studies on plant-pathogen interactions are very important to understand the molecular mechanism of insect resistance or disease resistance in plants so that adequate precautions can be taken to prevent crop loss in agriculture. It was observed that plants can synthesize certain polypeptides in response to a microbial attack as was demonstrated in the case of the tobacco plant when attacked with the tobacco mosaic virus. These proteins are called pathogen-related proteins or PR proteins.

In addition to the formation of PR proteins, an array of other defense-related responses such as production of enzymes responsible for the expression of genes related to the phytoalexins synthesis, wall-bound phenolics, hydrolyzing enzymes, and hydroxy-proline rich glycoproteins were detected.

These metabolites were synthesized and accumulated around the site of infection for preventing the entry of the invading organism. These information will help in devising strategies, including genetic engineering, to protect crop plants from disease and attack of insects, thus to reduce the crop loss.

Tags: Bio Technology, Bio Genetics, Immune System

What is Apoptosis of Cells

What is Apoptosis?

Apoptosis is defined as programmed cell death, which occurs very systematically.

Normally cell death can occur in two ways. One is by this apoptosis and the other is by necrosis, which occurs under pathogenic conditions or deficiencies.

Apoptosis is a highly ordered process. During apoptosis the cells are disassembled very systematically. They detach from the neighboring cells of the tissue and its protoplasm condenses. The membrane-bound organelles such as mitochondria disintegrate by releasing its contents into the cytoplasm. The enzymes, endonucleases, act on the chromatin materials and break the DNA into fragments. At the final stage the cell membrane starts forming blebs and the cell fragments into apoptosis bodies.

This type of cell death is a process of normal physiology and always occurs during organ development. Compared to apoptosis necrosis occurs in a disordered manner and occurs due to the action of toxins produced by the pathogens on the cell.

Tags: Bio Technology, Bio Genetics, Immune System

Understanding the Defense Mechanisms in Plants

Defense Mechanisms in Plants:
Like animals, plants are also exposed to a wide variety of enemy organisms, which can damage the plants. These organisms include insect pests, nematodes, pathogenic fungi, bacterium, viruses and many other organisms. Plants are also exposed to many types of environmental stress called abiotic stresses. The stress of living organisms is known as biotic stress. Biotic stress can cause a severe reduction in the quantity as well as quality of the crops. In spite of the attack by pathogenic organisms and other animals, they remain healthy. This is because plants also have a defense mechanism to fight against the invading organisms. Studies about plant-defense mechanisms are very important because the identification and isolation of any genes related to the defense response can be used for genetically engineering other crop plants if needed. The defense system can be classified into two categories based on the defense response: passive or constitutive if it is a preexisting method of response and active or inducible if the method of response is a new type developed after the infection or attack by the pathogen.

Passive Defense:
This type of defense response is due to the presence of some structural components or some type of metabolites present in the body of the plant. The outer covering of the plant surface may be a special type such as cuticle or wax, which cannot be attacked or digested by the infecting fungus or bacteria. The presence of strong material such as lignin, tough bark, cuticle, etc. can effectively prevent the organisms from penetrating the plant surface. There are a large number of secondary metabolites such as alkaloids, tannins, phenols, resins, etc., which are toxic to pests and pathogens. Some of these compounds may have antimicrobial, antibacterial, or insecticidal properties. In addition to the secondary metabolites, there are certain proteins or peptides that have antimicrobial properties. For example, the antifungal pep tides present in the seeds, which help in preventing the seeds from fungal infection; hydrolytic enzymes, which can lysing the bacteria and fungus; and proteins that inactivates the viral particle by digesting its coat protein and nucleic acids.

Active Defense :
The defense response, which is produced newly and is not present previously in the cell or body, is called the active defense. The plant-cell wall is one of the sites where the change due to the defense response can be observed. All changes that happen in the cell wall due to an infection are collectively known as wall apposition. When a microorganism such as a fungus or bacteria starts infecting the plant body through the surface, immediately cell-wall thickness at that part is increased to make the penetration impossible. The change in thickness is due to the addition of new wall materials to the cell wall, specifically to the area of infection. Another interesting mechanism or response is called hypersensitive response (HR). In this response, the cells around the site of infection become necrotic. The metabolic activities of these cells also change. Their respiration becomes very slow or completely stopped. They begin to accumulate toxic compounds. Thus, an inhibitory effect or an unfavorable condition is created for the further growth and spread of the pathogen around the site of infection. The plant system or those cells (cells around the site of infection) also produce certain new chemicals in response to the infection known as phytoalexins. Phytoalexins are small molecular weight compounds produced when there is microbial attack or under conditions of stress, which are completely absent in healthy tissues.

It has been experimentally observed that if the phytoalexins production by an infected tissue is blocked or inhibited using some selective inhibitors, the resistance of the plant against the infection has reduced substantially. Similarly, it has been demonstrated that those pathogens, which can produce the enzyme for degrading the phytoalexins, had a pathogenisity that was very high compared to those that cannot produce such enzymes.

Tags: Bio Technology, Bio Genetics, Immune System

Know the Immune Response

What is immune response?
The immune response is the protective response against the invading microorganism shown by the immune cells. When a foreign cell enters the body, the body fluid, lymph, takes these cells to the lymph nodes. The lymph nodes are the filter-like organs scattered in several parts of the body. The lymph nodes contain all the cell components of the immune system-B-cells, T-cells, and macrophages. The macrophages engulf the pathogen and are digested by the enzymes present in the lysosomes of the macrophages. These digested components of the pathogens are presented to the lymphocytes. Then a number of cellular mechanisms occur and a number of substances are secreted as a result of the immune response, which is based on the nature of the antigen (the degraded product of the pathogen). Basically, there are two types of immune response, which is dependent on two cellular systems: the humoral or circulating antibody system, (B-cells immunity), and cell-mediated immunity, (T-cells immunity).

Both immune responses work by identifying antigens (foreign proteins or polysaccharides) either as part of a virus or bacterium or as a partially degraded byproduct. Both systems also recognize human antigens not made by the individual resulting in graft rejection.

The humoral antibody system (B-cell response) produces secreted antibodies (proteins), which bind to antigens and identify the antigen complex for destruction. Antibodies act on antigens in the serum and lymph. B-cell-produced antibodies may either be attached to B-cell membranes or free in the serum and lymph. The cell-mediated system acts on antigens appearing on the surface of individual cells. T-cells produce T-cell receptors, which recognize specific antigens, bound to the antigen presenting structures on the surface of the presenting cell.

Humoral-Antibody System: B-cells
Each B-lymphocyte, or B-cells produces a distinct antibody molecule (immunoglobulin or Ig). Over a million different B-lymphocytes are produced in each individual. Thus, each individual can recognize over a million different antigens. The antibody molecules are glycoproteins in nature and each one is composed of two copies of two different proteins. There are two copies of a heavy chain, over 400 amino acids long, and there are two copies of a light chain, over 200 amino acids long. There are five different kinds of antibodies. They are IgG, IgM, IgA, IgD, and IgE. Each antibody molecule can bind two antigens at one time, thus, a single antibody molecule can bind to two viruses, which leads to clumping. When a new antigen comes into the body, it binds to the B-cell, which is already making an antibody that matches the antigen. The antigen-antibody complex is engulfed into the B-cell and partially digested. The antigen is displayed on the cell surface by a special receptor protein (MHC II) for recognition by helper T-cells. The B-cell is activated by the helper T-cell to divide and secrete antibodies, which circulate in the serum and lymph. Some B-cells become memory cells to produce antibody at a low rate for a long time (long-term immunity) and to respond quickly when the antigen is encountered again. The response is regulated by a class of T-cells called suppressor T-cells.

Cell-Mediated System: T-cells :
T-cells mature in the thymus, which is why it is called a T-cell. A large number of different kinds of T-cells, each producing a different receptor in the cell membrane, are present in the system. Each receptor is composed of one molecule each of two different proteins. Each receptor binds a specific antigen but has only one binding site. Receptors recognize only those antigens, which are "presented" to it by another membrane protein of the MHC type (major histocompatibility complex). T-cell receptors recognize antigens presented by B-cells, macrophages, or any other cell type. T-cells, B-cells, and macrophages use MHC-II receptors for presentation; all other cells use MCH-I (responsible for most of tissue graft rejection). When a T-cell is presented with an antigen, its receptor binds to the antigen and it is stimulated to divide and produce helper T-cells to activate B-cells with bound antigen, suppressor T-cells to regulate the overall response, and cytotoxic "killer" T-cells to kill cells with antigen bound in MHC-I.

Tags: Bio Technology, Bio Genetics, Immune System

Understanding of Immune System in Animals & Humans

Firstly let us try to understand as to what is Immune Response:

All living organisms whether plants or animals or microbes are always prone to the attack of pathogenic organisms such as bacteria, fungi, viruses and other type of parasitic protozoans. There is a well-developed defense mechanism in humans and animals to fight against these parasitic and pathogenic organisms. This defense mechanism in humans and animals is known as immune system and the protective response of the body against the invading organism is called the immune response. The immune system always guards the body against the various types of microbes and parasites present in the environment. If the immune system is not responding properly, even a minor infection can become fatal.

The Immune System :
The immune system is well developed and is very complex in mammals and higher forms of vertebrates. The complexity of the immune system decreases as we go down the evolutionary scale. Organisms such as birds, reptiles, amphibians, fish, etc. have comparatively simple types of immune systems. There is no immune system in invertebrates such as starfish, hydras, earthworms, insects, etc. The immune system consists of certain specialized cells known as immune cells and certain specialized organs called lymphoid organs. The lymphoid organs in which ' the immune cells originate and mature are called the primary lymphoid organs, which include bone marrow and thymus. After maturation they migrate to other organs, the secondary lymphoid organs, where they settle down and function. These organs include the lymph nodes and the spleen.

The immune cells are distributed all over the body. Some of them reside in tissues and others circulate in the body through body fluids such as blood and lymph. The cells that carry out the immune response include phagocytic cells and natural killer cells (NK). The phagocytic cells include the white blood cells or lymphocytes and the macrophages. The macrophages engulf the invading organisms. The lymphocytes are the main immune cells and are further divided into different types. Morphologically, all lymphocytes are identical and cannot be distinguished. They can be classified based on the presence of certain specific molecules on the surface of the cell membrane and the function they perform. The most important lymphocyte groups are B-Iymphocytes or B-cells and T-Iymphocytes or T-cells.

Macrophages consist of different types of phagocytic cells. They are neutrophils, eosinophyls, and basophyls. These phagocytic cells are also called granulocytes because of the presence of granules in the cytoplasm and because they have a multi-lobed nucleus. There is another cell without any granules in the cytoplasm and without any lobes in the nucleus. These cells are called monocytes. Monocytes are the precursors of macrophages present in the tissues. The monocytes migrate into the tissues from blood and change into macrophages. Macrophages are large cells with extensive cytoplasm and have many vacuoles. The macrophages of tissues are generally called histiocytes. Those macrophages present in the liver tissues are called kupfer cells, those present in linings is known as alveolar, and those present in the peritoneal cavity are called peritoneal macrophages.

Tags: Bio Technology, Bio Genetics, Immune System

Wednesday, January 14, 2009

How does Development Take Place in Plants

The process of double fertilization results in the formation of zygote and an endosperm cell inside the embryo sac of ovule. The ovule is within the oyary. The zygote follows series of mitotic cell divisions and differentiates into a small plant later known as the embryo. The endosperm cell develops into the endosperm or the cotyledons. Ovules develop into the seed and the ovary forms the fruit.

The zygote within the embryo sac undergoes a number of repeated mitotic divisions to form a group of cells surrounded by the endosperm tissue, which is also under development. This structure is known as the proembryo. In the proembryo the cells are arranged in three layers:

# Protoderm, which forms the surface tissues such as the epidermis.
# Procambium, which forms the vascular tissues.
# Ground meristem, which gives rise to ground tissues.

At this stage, the embryo takes on the shape of an axis with meristems at both ends. These meristems are the apical shoot meristem and the apical root meristem, from which structures of the shoot system and root system will ultimately develop. In addition, two bumps appear near the anterior; these are the two cotyledons, characteristic of dicot embryos. The cotyledons rapidly elongate, and the embryo is divided into regions, with respect to the cotyledons. The region above the attachment of the cotyledons is the epicotyl, which contains the apical shoot meristem.

The region below the attachment of the cotyledons is the hypocotyl, which ends with the radicle, containing the apical root meristem. Typically, the embryonic axis will have to fold, to fit within the embryo sac. Endosperm may or may not be absorbed into the cotyledons. It may be consumed completely in the maturation of the embryo, or some may remain for germination. One of the main differences in the growth and development ?f plant systems from that of animal tissues is that in plants the growing ends or the meristems are very small but repeated many times above the ground as the terminal parts of shoot systems. These meristems are always active and never stop their embryonic nature. Because of this they continue to produce new tissues and cells throughout their life.

Tags: Bio Technology, Bio Genetics, Plant Development

How does Development take place in Animals

The developmental pattern of a fertilized egg into an embryo is almost identical in all animal forms at least in the initial stages. Following fertilization, the zygote undergoes a series of divisions that leads from a single cell to a collection of cells in the form of a hollow sphere, known as blastula. The cells increase in number very rapidly at the same time the size of the cells decreases. During this period some of the blastula cells begin to differentiate into endoderm, mesoderms and ectoderm.

The endoderm generally gives rise to epithelial lining of the gut, the mesoderm forms the muscles, internal skeleton; and the ectoderm develops into nerves and the outer covering of the animal. During this stage there is the rearrangement in the position of the cellular layers by a process known as gastrulation. After gastrulation the endoderm becomes the innermost layer of cells and the mesoderm surrounds the endoderm and the outermost layer is the ectoderm. Endoderm can further specialize into liver, pancreas, lung or many other cell types, but cannot reverse course and become ectoderm or mesoderm. This stage of embryo is known as gastrula. There is no significant growth in size between zygote and gastrula. All these stages are so important that all vertebrates, in spite of their great anatomical and physiological differences, follow this developmental pattern.

Once the gastrulation has taken place with the rearrangement of different layers, the cell differentiation starts rapidly. The three layers of cells differentiate and develop into various organs needed to make a functional individual. Just three weeks after fertilization, human embryos will develop a heart and by the eighth week of development the head is completely identifiable in an embryo with a 2.5 cm length. Almost all types of tissues and organs start developing by this time. By the twelfth week of development it develops external recognizable parts such as sex organs, fingers, nails, and toes. A gut also develops from the endoderm during this period.

How does an animal develop from a single cell? The answer to this fundamental question of embryology and developmental biology is based on asymmetry in the egg cell and instructions in the DNA of the developing animal. Structures form in the developing embryo under the guidance of the DNA instructions that are the same in each cell, and external cues that let the cell know where it is and what type of cell it should become. Signals include information from neighbor-neighbor contact and from gradients of protein or small-molecule morphogens.

Tags : Bio Technology, Bio Genetics, Animal Development

Know the Mechanism of Reproduction in Humans


Reproduction in humans occurs only by sexual methods.

The gametes in human reproduction are the sperm and egg. Sperms are the male gametes and egg is the female gamete. Both are produced after meiosis and therefore are haploid. Humans are unisexual and thus male and female gametes are produced in separate individuals. Humans have a pair of primary reproductive organs; sperm-producing testes in males and egg-producing ovaries in females, along with accessory ducts and glands. Testes and ovaries also produce hormones that influence reproductive functions and secondary sexual traits.

The hormones testosterone, LH (luteinizing hormone), and FSH, (follicle stimulating hormone) control sperm production. The hormones estrogen, progesterone, FSH, and LH control egg maturation and release, as well as changes in the lining of the uterus, the endometrium. The testis is an ovoid-shaped gland consisting of coiled tubules called seminiferous tubules. The testes are placed in a scrotal sac outside the abdominal cavity. The male gametes or sperms are produced in seminiferous tubules by a complex process called spermatogenesis. Sperm produced in the testes are carried to the copulating organ, the penis via epididymis (stores sperm until they have matured) and vas deference. Vas deference is a straight tube, which along with spermatic artery and vein, forms the spermatic cord. Seminal vesicle, prostate gland, Cowper's gland, etc. are the accessory parts present along with male genital organs.

The female reproductive organs consist of ovaries and fallopian tubes. Ovaries produce the female gamete ovum (egg) and fallopian tubes are a pair of ducts, one from each ovary, that catches the ovum released at ovulation each month. This tube carries the egg and houses the fertilized egg through its embryonic development and is lined with smooth muscle, which contracts, moving the ovum toward the uterus. The fertilization of ovum with sperm usually occurs in this tube and the initial development of resulting zygote into an embryo also occurs here. The uterus is lined with endometrium; this is where the embryo implants and completes its development the cervix is the muscular ring at the mouth of the uterus and the vagina is a thin-walled chamber into which sperm are directly deposited during intercourse. The urethra is part of the female urinary tract, but not part of the female reproductive tract, unlike males. The production of sperm is a continuous process starting from puberty and lasting throughout life in males. But in females the production of female gamete or the egg is a cyclic process with a periodicity of about 28 days. During these periods there is a great change in the structure and function of the entire reproductive system. At birth, the female has about 2 million primary oocytes, which give rise to what will become a mature egg, or ovum. Unlike the male, no more primary oocytes or cells that will give rise to a mature gamete are produced after a female is born. At birth the primary oocytes are in a resting state and will not develop any further until they are triggered by the hormone FSH released from the pituitary, at which point a few at a time will resume meiosis. Only 400 of the original 2 million primary oocytes actually develop into mature eggs.

During copulation sperm is deposited near the cervix in the vagina. These sperms are motile and active for some times-at least for three days. They move toward the fallopian tubes where they may come in contact with the egg cell. During fertilization, the sperm cell injects its nucleus into the cytoplasm of the oocyte and fertilization takes place. Only one sperm can fertilize an egg and further fusion with sperm is prevented. By fertilization the diploid number of chromosomes is restored in the fertilized egg, which is known as the zygote. The zygote starts its development in the fallopian tube and continues its development in the uterus.

Tags: Bio Technology, Bio Genetics, Human Reproduction

Sexual Reproduction in Animals

Sexual reproduction is the most common method of reproduction in higher forms of animals. Sexual reproduction involves the formation of male and female gametes and their fusion resulting in the formation of a zygote. The gametes are produced after the meiosis and are haploid and the fusion product of gametes, the zygote, is diploid. The process of syngamy or fertilization causes the mixing of genetic materials of the male and female parent.

Animal development commonly proceeds through several stages. Gametogenesis, during which the egg and sperm mature within the reproductive organs of the parents. Fertilization, which begins when a sperm penetrates an egg and is completed when the sperm and egg nuclei fuse forming a zygote. The zygote undergoes mitotic cell divisions that form the early multicellular embryo, which develops into an organism gradually through different stages. Sexual reproduction thus shows the formation diploid and haploid stages in the life cycle alternately.

The two types of gametes-the male gametes and female gametes-may be produced in the same body or separately by the male and female parent. When separate male and female individuals are present in a species, they are called unisexual organisms. All higher forms of animals and humans are examples. Some species are capable of producing both male and female gametes in the same organisms (body) and such species are known as bisexual or hermaphrodites. Some lower forms of organisms such as earthworms, tapeworms, snails, and some fish belong to this class.

Tags : Bio Technology, Bio Genetics, Sexual Reproduction

Asexual Reproduction in Animals

In animals the asexual reproduction is limited to unicellular and lower forms organisms. Following are the different methods of asexual reproductions.

1) Binary fission:
The parent cell divides into two or more daughter cells by a cleavage of the protoplast after the nuclear division. Normally two identical cells are formed. Therefore, it is known as binary fission. It is usually observed in organisms such as plasmodium, paramecium, amoeba, etc. When the parent cell is divided into a number of progenies it is called multiple fission. First, the nucleus undergoes repeated division, which is followed by cytoplasmic division into a number of daughter cells. The cell undergoing multiple fission is called schizont and the process is known as schizogamy.

2) Budding :
Here, offspring develops as a growth on the body of the parent. In some species (e.g., jellyfishes) the buds break away and take up an independent existence. In others (e.g., corals) the buds remain attached to the parent and the process results in colonies of animals. Budding is also common among parasitic animals such as tapeworms.

3) Fragmentation
In certain tiny worms, as they grow to full size, they spontaneously break up into eight or nine pieces. Each of these fragments develops into a mature worm and the process is repeated.

4) Parthenogenesis:
In parthenogenesis ("virgin birth"), the female produces eggs, but these develop into young without ever being fertilized. Parthenogenesis occurs in some fishes, several kinds of insects, and a few species of lizards. In a few species it is the only method of reproduction, but more commonly animals turn to parthenogenesis only at certain times. For example, aphids use parthenogenesis in the spring when they find themselves with ample food. Reproduction by parthenogenesis is more rapid than sexual reproduction, and the use of this mode of asexual reproduction permits the animals to quickly exploit the available resources.

Parthenogenesis is forced on some species of wasps when they become infected with bacteria such as the genus Wolbachia. In these wasps (as in honeybees), fertilized eggs (diploid) become females; unfertilized (haploid) eggs become males. However, in Wolbachia-infected females, all their eggs undergo endoreplication producing diploid eggs that develop into females without fertilization; that is, by parthenogenesis. Treating the wasps with an antibiotic kills off the bacteria and "cures" the parthenogenesis.

Tags: Asexual Reproduction, Bio Technology, Bio Genetics

Plant Propagation

Commercially important plants are often deliberately propagated by asexual means in order to keep particularly desirable traits (e.g., flower color, flavor, resistance to disease etc.). Grafting is widely used to propagate a desired variety of shrub or tree.

All apple varieties, rose varieties, for example, are propagated this way. Apple seeds are planted only for the root and stem system that grows from them. After a year's growth, most of the stem is removed and a twig (scion) taken from a mature plant of the desired variety is inserted in a notch in the cut stump (the stock).

So long as the cambiums of scion and stock are united and precautions are taken to prevent infection and drying out, the scion will grow. It will get all its water and minerals from the root system of the stock. However, the fruit that it will eventually produce will be identical (assuming that it is raised under similar environmental conditions) to the fruit of the tree from which the scion was taken. Cuttings may be taken from the parent and rooted. The same method of grafting is applicable in the case of rubber plantations.

Tags: Bio Genetics, Bio Genetics, Plant Propagation

Monday, January 12, 2009

What is Vegetative Reproduction in Plants

It is reproduction by mitosis allowing a new, genetically identical individual to be produced. When a very desirable combination of traits is found, sexual reproduction risks losing them in the randomness of the process. Asexual reproduction does not allow genetic variation, but guarantees reproduction (no dependence on others). It rapidly increases the numbers of an organism and keeps its desired combination of traits. Many plants use a combination of sexual and asexual reproduction to get the benefits of both methods.

Most plant organs have been used for asexual reproduction, but stems are the most common.

Stems: In some species, stems arch over and take root at their tips, forming new plants. The horizontal aboveground stems, called stolons in certain plants like that of the strawberry, produce new daughter plants at alternate nodes. Various types of underground stems such as rhizomes, bulbs, corms, and tubers are used for asexual reproduction as well as for food storage.

Leaves: Leaves of certain plants like that of the common ornamental plant bryophyllum acts as the organs for vegetative multiplication. Mitosis at meristems 'along the leaf margins produce tiny plantlets that fall off and can take up an independent existence.

Roots: Some plants use their roots for asexual reproduction. The dandelion is a common example. Trees, such as the poplar, send up new stems from their roots. Sometimes, an entire grove of trees may form all part of a clone of the original tree.

Tags: Bio Technology, Bio Genetics, Reproduction in Plants

Mechanisms of Pollination in Animals & Insects


There are two mechanisms whereby pollination occurs:

Animal pollination or insect pollination. Food or another reward is provided and "advertised" via color or fragrance. This mechanism can be effective in promoting pollination even in sparse populations.

Wind pollination requires dense populations.

Self-pollination (which would result in inbreeding) is frequently prevented in plants, even though they might have perfect flowers. Flowers may be imperfect, plants may be dioecious, or compatibility genes might be required for successful pollination to occur.

Once pollination occurs, the pollen coat ruptures and the pollen tube grows downward through the style to the ovary. Once it enters the embryo sac via the micropyle, the pollen nuclei migrate downward through the tube and double fertilization occurs.

Tags: Bio Technology, Bio Genetics, Pollination

Wednesday, January 7, 2009

Ways of Reproduction in Plants

rIn higher plants there are mainly two methods of reproduction-sexual reproduction that involves the formation of gametes and asexual or vegetative reproduction, in which there the vegetative parts are used for propagation.

Sexual Reproduction
Typically, plant life history involves alternation of generations, during which a diploid sporophyte gives rise to a haploid gametophyte. The gametophyte generation produces gametes that, through syngamy (fusion of gametes during fertilization), provide for another generation of diploid sporophytes, to continue the cycle. The sporophyte does not produce gametes but rather, meiosis occurs in spore mother cells and produces haploid spores. These spores divide mitotically to form gametophytes, which subsequently produce gametes via mitosis. Within the plant kingdom the dominance of phases varies. In nonvascular plants such as mosses and liverworts, the gametophyte phase is dominant. Vascular plants show a progression of increasing sporophyte dominance from the ferns and "fern allies" to angiosperms.

In angiosperms, flowers are the organs of reproduction. A typical flower has four parts arranged in circles: sepals, petals, androecium, and gynoecium from periphery to center. Androecium and gynoecium are the male and female reproductive organs.

The male reproductive organ of the flower is composed of units called stamens. Each stamen consists of a filament and an anther. The anther produces the male spores called pollen grains.

The female reproductive organ consists of units called pistils. Each pistil consists of terminal filament called style with stigma at its terminal part and an ovary, from which the style starts. The ovary contains ovules. The flowers may be bisexual with both male and female organs in the same flower, or it may be unisexual with anyone type of sex organs. The male flowers are the staminate flowers and the female flowers are the pistillate flowers.

Tags: Bio Genetics, Bio Technology, Reproduction

Tuesday, January 6, 2009

Various Processes of Genetic Recombination in Bacteria

Following are the three processes by which genetic recombination can occur in bacteria.

There is no contact between the donor cell and the recipient cell. It is the random picking of DNA fragments released by some other cells. The recipient cell actively takes the DNA fragment and inserts it into the genome of the recipient bacteria.

This is the DNA transfer between two bacteria through a long protoplasmic connection established between the cells. Conjugation occurs between two different types of bacteria known as positive and negative strains, equivalent to male and female cells. They are called F+ and F-. The donor or the F+ strains of bacteria harbor a circular molecule of DNA known as F factor (F for fertility) or the sex factor. This factor is absent in the F-strains. The presence of F factor is responsible for the presence of a special type of pilus, known as F pilus or sex pilus. The sex pilus is responsible for the formation of the cell-to-cell contact and the formation of the protoplasmic connection, known as the conjugation tube, between the cells. After the establishment of the conjugation tube, one of the strands of the F-factor DNA passes through the sex pilus or the conjugation tube from the donor (F+) to the recipient (F-). In some cases, the F factor plasmid gets integrated with the genomic DNA and mobilizes the transfer of the genomic DNA to the recipient. Since such strains show high-frequency recombination, they are called Hfr strains.

This is another important type of genetic recombination in bacteria which takes place through bacteriophages. A fragment of DNA is transferred to a recipient through a bacteriophage. A bacteriophage is a virus, which infects bacteria. When a bacteriophage infects a bacterium, it injects its DNA into the bacterial cell and it gets integrated with the bacterial DNA. This phage DNA undergoes multiplication along with bacterial DNA. After some multiplications, the phage DNA comes out of the bacterial genome and will be encapsidated in protein coats to daughter phages. In this process a small bit of bacterial DNA will also be taken along with phage DNA. When this phage infects another bacteria, the DNA bit of the old bacterial host will be transferred to the new bacterial genome & causes a genetic recombination. The old bacterial host is the genome and the new bacterial host of the phage is the recipient.

Key words: Bio Genetics, Bio Technology, Genetic Recombination

How the reproduction takes place In Living Organisms

Reproduction is one of the most important characteristics of living organisms. It can be defined as the ability of microorganisms to produce individuals of the same species. This process transfers the genetic material from the parental generation to the next generation. Reproduction is necessary to maintain the genetic continuity among a species and it allows the increase in the total number of members in a species or variety. The process of reproduction involves the participation of special types of cells and processes of cell division involving genetic recombination. Therefore, reproduction can act as means to generate genetic variations and diversity among species.

There are different methods of reproduction among various types of living organisms. It can be broadly classified into asexual reproduction, sexual reproduction, and vegetative reproduction.

Reproduction in Microbes :
Microorganisms such as bacteria and other single-celled organisms mainly reproduce by asexual methods. In bacteria, a single organism divides into two identical cells, the progenies. This type of asexual reproduction is called binary fission. By this reproduction, the number of bacteria increases exponentially and this phase of growth is called the exponential growth phase or logarithmic growth. In the asexual method of reproduction there is no mixing of genetic materials of two cells; therefore, all progenies are of the same genetic makeup. If any variation is observed in the population of an asexually reproducing organisms, it may be due to random variations caused by mutation that occurs during DNA replication.

There is a primitive type of sexual reproduction in bacteria known as conjugation. It does not involve the fusion of any gametes or fertilization. But the essential feature of sexual reproduction, namely genetic recombination (mixing of genetic material), occurs. During the process of conjugation a part of genetic material (DNA) is transferred to the recipient cell through a temporarily formed conjugation tube established between the cells.

Keywords: Bio Genetics, Bio Technology, Reproduction

Know the Thermoregulation in Plants

Regulation of temperature is known as thermoregulation. It is almost as important as osmoregulation. Biochemical reactions of the cells are taking place under an optimal temperature. Therefore, the stability of the optimal body temperature is very essential for the normal functioning of all biological reactions. The variations in the body temperature can affect the functioning of the organisms in a very lethal way. Depending on the influence of the environmental temperature on the body temperature the animals can be of two types: ectotherms and endotherms organisms.

Ectotherms: use the external environment and behavioral mechanisms to maintain a thermal balance as much as possible. But their metabolic machinery must be generalized. The enzymes and metabolic reactions have to be functional in a wide temperature ranges. Their enzymes have the ability to work in a wide range of temperatures. For example, insects tend to be maxitherms when given the choice (fish, to digest, move down to cooler temperatures to digest food, while feeding in warm surface waters). Many ectotherms show behavioral and structural adaptations, which help them to adjust to temperature changes. For example, amphibians undergo hibernation during the hot summer. Another example, marine iguanas, feed in cold ocean waters, where they lose heat quickly. They try to gain heat by orienting their black-colored body parts directly to the radiant heat of sun. They also try to get heat by pressing their belly against the rocks that have been warmed by the sun.

Endotherms: are organisms that have a constant body temperature and use a variety of physiological mechanisms to maintain a constant internal temperature. The basic mechanism is to have a constantly active metabolic machine. Endotherms such as mammals and birds have very effective temperature control methods. They have a very high respiratory rate, which generates metabolic heat. They also conserve heat by minimizing the heat loss. The heat loss can be minimized by decreasing conductivity or by increasing insulation, or by vasoconstriction or vasodilatation, or by changing the color of insulation. For example, feathers. Air trapped in fur or feathers acts as an insulator, which prevents the loss of heat.

Panting by birds and mammals and sweating in mammals are effective methods for cooling the system. In certain organisms minimized respiration prevents the loss of excess heat from the body. In mammals there is the mechanism of thermogenesis by shivering, a type of active thermoregulation controlled by the hypothalamus of the brain through a negative feedback thermostat.

There are some leaves with a shiny leaf surface to cut down the radiant heat by reflection. Certain desert plants are provided with folded ridges on the trunks, so that sunlight falls only at shallow angles resulting in reduced absorption of radiant heat.

All living organisms are provided with different structural and physiological modifications and adaptations to maintain homeostasis.

Key words: Bio Genetics, Bio Technology

Regulation of Water Balance in cells and organisms

Water is a very important element of life. There is a constant and steady loss of water from the body in different ways. For example, transpiration and excretion can reduce the water content of the body substantially and therefore should be replaced. Water is the medium for biochemical reactions and is needed in sufficient quantities for the easy diffusion and flow of dissolved and suspended materials within the body. A disturbance in the water balance in the body can disturb entire metabolic activities.

In animals, the site of homeostasis is the kidney. Kidneys are concerned with the isolation and excretion of metabolic waste products. Kidneys filter a large volume of water, solutes, and wastes everyday. But major amounts of water and solutes are reabsorbed. Only a small amount of water, solutes, and all wastes are excreted as urine. This is enough to create a shift in the water balance of the body. But we take in a lot of water along with food and otherwise. In the case of fresh water fishes, since the solute concentration in the cells is higher than the surrounding water excess water gets into their cells. The excess water is removed by excreting very dilute urine. Whereas, fish living in salt water have a different mechanism for water regulation. They take in a lot of salt water and the excess salt is pumped out through their gills. This is an active mechanism and needs lot of energy. In addition to this they produce highly concentrated urine in their specialized kidneys. Thus, they can remove a lot of salt by conserving water. This is the mechanism of homeostasis in marine organisms.

In plants, different mechanisms and modifications regulate water loss.

Terrestrial plants regulate water balance through roots and leaves. For example, during dry conditions certain plants drop their leaves to check water loss. In certain soil conditions where there is high salt concentration, certain plants actively pump minerals through their roots, which increases the solute concentration of the cell sap in the root hair. As the salt concentration is higher in the cell sap, water diffuses into the cell by osmosis. Plants have several mechanisms to conserve water. In desert plants, there is a very thick waxy coating all over the body to prevent water loss by evaporation. In most cases, stomata are located on the lower side of the leaves and also there is mechanisms to close the stomata during the day in those plants that are growing in dry weather.

Key words: Bio Genetics, Bio Technology

Understanding of Translocation in Plants

The transport of sap containing dissolved products of photosynthesis through phloem is called translocation. Translocation is the transport of the products of photosynthesis by phloem to the rest of the plant. In angiosperms, sieve-tube members are the specialized cells of phloem that function in translocation. Sieve-tube members are arranged end-to-end forming long sieve tubes. Porous cross walls called sieve plates in between the members allow phloem to move the solution freely along the sieve tubes.

Phloem sap contains primarily sucrose, but also minerals, amino acids, and hormones. Phloem sap movement is not unidirectional; it moves through the sieve tubes from source to the sink. Source is the organ where sugar is produced by photosynthesis or by the breakdown of starch (usually leaves) and sink is the organ that consumes or stores sugar (growing parts of plant, fruits, non-green stems and trunks, and others). Sugar flows from source to sink. Source and sink depend on season. A tuber is a sink when stockpiling in the summer, but it is a source in the spring. The sink is usually supplied by the closest source. Direction of flow in phloem can change, depending on locations of source and sink.

Key words: Bio Genetics, Bio Technology