Karyotype

Karyotyping is the process by which cytogeneticists take photographs of chromosomes in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalies. The term is also used for the complete set of chromosomes in a species or in an individual organism and for a test that detects this complement or measures the number.In our view, it is unlikely that one process or the other can independently account for the wide range of karyotype structures that are observed ... But, used in conjunction with other phylogenetic data, karyotypic fissioning may help to explain dramatic differences in diploid numbers between closely related species, which were previously inexplicable.We have a very poor understanding of the causes of karyotype evolution, despite many careful investigations ... the general significance of karyotype evolution is obscure.They simply could not believe what they saw ... They kept quiet for two or three years because they thought something was wrong with their tissue culture ... But when they obtained a couple more specimens they confirmed .Polyploidy in animals is much less common, but it has been significant in some groups. Karyotyping is the process by which cytogeneticists take photographs of chromosomes in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalies. The term is also used for the complete set of chromosomes in a species or in an individual organism and for a test that detects this complement or measures the number. 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).p28 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. The study of karyotypes is important for cell biology and genetics, and the results may be used in evolutionary biology (karyosystematics) and medicine. Karyotypes can be used for many purposes; such as to study chromosomal aberrations, cellular function, taxonomic relationships, and to gather information about past evolutionary events. Chromosomes were first observed in plant cells by Carl Wilhelm von Nägeli in 1842. Their behavior in animal (salamander) cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, Heinrich von Waldeyer in 1888. It is New Latin from Ancient Greek κάρυον karyon, 'kernel', 'seed', or 'nucleus', and τύπος typos, 'general form'). The next stage took place after the development of genetics in the early 20th century, when it was appreciated that chromosomes (that can be observed by karyotype) were the carrier of genes. Lev Delaunay  in 1922 seems to have been the first person to define the karyotype as the phenotypic appearance of the somatic chromosomes, in contrast to their genic contents. The subsequent history of the concept can be followed in the works of C. D. Darlington and Michael JD White. Investigation into the human karyotype took many years to settle the most basic question: how many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism. Painter in 1922 was not certain whether the diploid of humans was 46 or 48, at first favoring 46, but revised his opinion from 46 to 48, and he correctly insisted on humans having an XX/XY system. Considering the techniques of the time, these results were remarkable.