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

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

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.

Androecium:
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.

Gynoecium:
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

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