Karyotype

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Karotypes

A karyotype is a preparation of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, sorted by length, centromere location and other features and for a test that detects this complement or counts the number of chromosomes. Karyotyping is the process by which a karyotype is prepared from photographs of chromosomes, in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalities.

Karyotypes describe the chromosome count of an organism and what these chromosomes look like under a light microscope. Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics. The preparation and study of karyotypes is part of cytogenetics.

The study of whole sets of chromosomes is sometimes known as karyology. The chromosomes are depicted (by rearranging a photomicrograph) in a standard format known as a karyogram or idiogram: in pairs, ordered by size and position of centromere for chromosomes of the same size.

The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). Thus, in humans 2n = 46.

So, in normal diploid organisms, autosomal chromosomes are present in two copies. There may, or may not, be sex chromosomes. Polyploid cells have multiple copies of chromosomes and haploid cells have single copies.

Karyotypes can be used for many purposes; such as to study chromosomal aberrations, cellular function, taxonomic relationships, medicine and to gather information about past evolutionary events (karyosystematics).

More information is available at [ Wikipedia:Karyotype ]
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