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

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