karyotype is the complete set of all chromosomes of a cell of any living organism. The chromosomes are arranged and displayed (often on a photo) in a standard format: in pairs, ordered by size and position of centromere for chromosomes of the same size. Karyotypes are examined in searches for chromosomal aberrations. It is used to determine other aspects of an individual’s genotype like sex (XX vs. XY pair). The study of karyotypes is known as karyology.
Normal human karyotypes are denoted 46,XX (for women) and 46,XY (for men). Hmyever. some individuals have other karyotypes with added or missing sex – chromosomes, including 47.X YY, 47.X XY, 47.XXX and 45,X. The karvotype 45,Y does not occur, as an embryo without an X chromosoiw cannot survive. Three types of techniques are used in karyotype analysis:
(a) Classic karyotype analysis
In the classic karyotype, a dye. Giemsa, 1; used. It stains bands on the chromosomes. This is also called G-bc.–rding. Each chromosome has a characteristic banding pattern. Tiles.: bands help to identik chromosomes. Two chromosomes of one pair have the same banding pattern.
Karyotypes are arranged with the short arm of the chromosome on top, and the long arm on the bottom. Some karyotypes call the short and long arms as p and q. respectively. The differently stained regions (and sub-regions) are given numerical designations from proximal to distal on the chromosome arms. For example. Cridu chat syndrome involves a deletion on the short arm of chromosome 5. It is written as 46,XX,5p-. The critical region for this syndrome is deletion of 15.2, which is written as 46,XX,5p15.2- or 46,XX,deR5p15.2).
Karyotype also shows individual chromosomes that match up with identical ones. There are some ‘cases where deletions, extra, or missing chromosomal material occurs. It causes diseases like Down syndrome, Angelman syndrome. Edwards syndrome and Paton syndrome.
Spectral karyotype (SKY technique)
Spectral karyotyping is a molecular cytogenetic technique. It is used to visualize all the 23 pairs of human (or the 20 pairs of mouse) chromosomes in different colors. This technique is widely used to identify stm_tural chromosome aberrations in cancer cells and other disease conditions. There are following steps of this technique:
1. Chromosome-specific DNA are labeled with different fluorophores. It produces fluorescently-labeled probes for each chromosome. But limited numbers of spectrally-distinct
fluorophores are available. Therefore, a combinatorial labeling method is used to genera e many different colors.
- Combinatorial labeling generates spectral differences. These spectral differences are captured and analyzed by using an interferometer attached to a fluorescence microscope.
- Image processing software then assigns a pseudo color to each spectrally different combination. It allows visualization of the individually’ colored chromosomes.
(c) Formation of Karyogram
‘Ibis technique is used to determine the (diploid) number of chromosomes of an organism. In this case, the cells are locked in metaphase in vitro with colchicine. Colchicine is a drug which prevents cytokinesis. These cells are then stained and photographed. They are arranged into a karyotype called karyogram. Like many sexually reproducing species. humans have special sex chromosomes. These are XX in females and XY in males. In Females, one of the two X chromosomes is inactive and can be seen under a microscope as Barr bodies.