Karyotype

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Related to Chromosome morphology: Karyogram

karyotype

[′kar·ē·ə‚tīp]
(cell and molecular biology)
The complement of chromosomes characteristic of an individual, species, genus, or other grouping.
An organized array of the chromosomes from a single cell, grouped according to size, centromere position, and banding pattern, if any.

Karyotype

 

chromosome set, the aggregate features of the chromosomes (numaber, size, shape, details of microscopic structure) in the cells of an organism of a given species.

The concept of the karyotype was introduced by the Soviet geneticist G. A. Levitskii in 1924. The karyotype is one of the most important genetic characteristics of a species, since every species has a particular karyotype that is different from that of related species (karyosystematics, a new branch of systematics, is based on this phenomenon). The fixed nature of the karyotype in the cells of a given organism is ensured by mitosis and, within a given species, by meiosis. The karyotype of an organism may change if the gametes are altered by mutation. The karyotype of individual cells sometimes differs from the species karyotype because of chromosomal or genomic somatic mutations. The karyotype of diploid cells consists of two haploid sets (genomes) from each parent; each chromosome of such a set has a homologue from the other set. The karyotype of males may differ from that of females in the shape (sometimes also in number) of the sex chromosomes, in which case they are described separately.

The chromosomes in a karyotype are studied during the metaphase stage of mitosis. The description of a karyotype must be accompanied by a microphotograph or sketch. In systematizing karyotypes, the pairs of homologous chromosomes are arranged (for example) in order of decreasing length, beginning with the longest pair. The pairs of sex chromosomes are put at the end of the series. Pairs of chromosomes of equal length are identified by the position of the centromere (primary constriction), which divides the chromosome into two arms, by the position of the nucleolar organizer (secondary constriction), and by the shape of the satellite. The karyotypes of several thousand species of plants (wild and cultivated) and animals and man have been studied.

REFERENCES

Rukovodstvo po tsitologii, vol. 2. Edited by A. S. Troshin. Moscow-Leningrad, 1966.
Lobashev, M. E. Genetika, 2nd ed. Leningrad, 1967.

IU. F. BOGDANOV

References in periodicals archive ?
The chromosome morphology was shown to be constant in the different Atta species, unlike the observations made for the species of Acromyrmex (Barros 2010; Cristiano et al.
Both chromosomes have heterochromatin on the centromere of this homeologous chromosome pair, while duplication of a portion of the centromeric heterochromatin may have modified the chromosome morphology.
Some of the differences in chromosome morphology seem attributable to undefined structural changes, but numerical change, as in Paphiopedilum, is due to whole-arm rearrangements.
Existing karyotypic descriptions for pholcid species (Table 1) show that the diploid number varies from 2n = 15 to 2n = 32, that the predominant chromosome morphology is metacentric and that the most frequent SDCS is of the X/XX type.
In this sense, the difference found in our data could be largely derived from the continuous changes of chromosome morphology produced during the cell cycle.
The cells were photographed under a Zeiss microscope and the chromosome morphology classification was determined according to Levan et al.