Information AboutKaryotype |
| CATEGORIES ABOUT KARYOTYPE | |
| chromosomes | |
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A karyotype is the observed characteristics (number, type, shape etc) of the chromosomes of an individual or species. In normal s, and may be used to determine other macroscopically visible aspects of an individual's Genotype , such as Sex . In order to be able to see the chromosomes and determine their size and internal pattern, they are chemically labeled with a dye ("stained"). The pattern of individual chromosomes is called chromosome banding, whereas the study of whole sets of chromosomes is known as '''karyology'''. Normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of Sex Chromosomes . Normal karyotypes for Women contain two X Chromosome s and are denoted 46,XX; Men have both an X and a Y Chromosome denoted '''46,XY'''. However, some individuals have other karyotypes with added or missing sex chromosomes, including 47,XYY , 47,XXY , 47,XXX and 45,X . The karyotype 45,Y does not occur, as an embryo without an X chromosome cannot survive. TYPES OF BANDING Molecular genetics employs several techniques to visualize different aspects of chromosomes:
probed for the Alu Sequence using FISH .]] CLASSIC KARYOTYPE In the "classic" (depicted) karyotype, a Dye , often Giemsa ''(G-banding)'', less frequently Quinacrine , is very used to stain bands on the chromosomes. Giemsa is specific for the Phosphate groups of DNA . Quinacrine binds to the Adenine - Thymine -rich regions. Each chromosome has a characteristic banding pattern that helps to identify them; both chromosomes in a pair will 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 ''p'' and ''q'', respectively. In addition, the differently stained regions and sub-regions are given numerical designations from Proximal to Distal on the chromosome arms. For example, Cri Du 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,del(5)(p15.2).1 SPECTRAL KARYOTYPE (SKY TECHNIQUE) Spectral karyotyping is a molecular Cytogenetic technique used to simultaneously visualize all the pairs of Chromosome s in an organism in different colors. Fluorescent ly-labeled probes for each chromosome are made by labeling chromosome-specific DNA with different Fluorophore s. Because there are a limited number of spectrally-distinct fluorophores, a combinatorial labeling method is used to generate many different colors. Spectral differences generated by combinatorial labeling 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, allowing the visualization of the individually colored chromosomes.E. Schröck, S. du Manoir, T. Veldman, B. Schoell, J. Wienberg, M. A. Ferguson-Smith, Y. Ning, D. H. Ledbetter, I. Bar-Am, D. Soenksen, Y. Garini, T. Ried. Multicolor spectral karyotyping of human chromosomes. ''Science'', 26 July 1996 ; 273 (5274):494. abstract This technique is used to identify structural chromosome aberrations in cancer cells and other disease conditions when Giemsa banding or other techniques are not accurate enough. CHROMOSOME ABNORMALITIES See Also: Chromosome abnormalities Chromosome abnormalities can be numerical, as in the presence of extra or missing chromosomes, or structural, as in Translocations , Inversions , large-scale deletions or duplications. Numerical abnormalities, also known as Aneuploidy , often occur as a result of Nondisjunction during Meiosis in the formation of a Gamete ; Trisomies , in which three copies of a chromosome are present instead of the usual two, are common numerical abnormalities. Structural abnormalities often arise from errors in Homologous Recombination . Both types of abnormalities can occur in gametes and therefore will be present in all cells of an affected person's body, or they can occur during Mitosis and give rise to a Genetic Mosaic individual who has some normal and some abnormal cells. Common chromosomal abnormalities that lead to disease include:
Some disorders arise from loss of just a piece of one chromosome, including
Chromosomal abnormalities can also occur in Cancer ous cells of an otherwise genetically normal individual; one well-documented example is the Philadelphia Chromosome , a translocation mutation commonly associated with Chronic Myelogenous Leukemia and less often with Acute Lymphoblastic Leukemia . SEE ALSO REFERENCES EXTERNAL LINKS
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