Karyotype is the name given to the set of chromosomes of a given species and has characteristic shape, size and number. The morphology of these chromosomes is constant for the species, however the number can vary in cases of chromosomal alterations.
→ Preparing the karyotype
When preparing the karyotype, the condensed chromosomes are arranged in pairs.. This organization makes it possible to evaluate all these structures of a particular species. In In humans, there are 46 chromosomes, which are arranged in 23 pairs.. The chromosomes that make up a pair have the same size and position of centromeres.
To prepare the karyotype, it is necessary to use somatic cells, as they are diploid. Then, a treatment is done to stimulate the mitosis and then these cells are cultured. Subsequently, cell division is interrupted in the metaphase, phase in which the greatest condensation of chromosomes is observed.
The cells are stained and analyzed using a microscope with a camera attached.By means of photography, the image of the chromosomes is arranged so as to organize each chromosome pair.
So we have the karyotype.→ Chromosome formula
The chromosomal formula is a way of describing the karyotype of an organism.The normal karyotype of the human species can be described as 46, XX or 46, XY, in which the first number of chromosomes is represented followed by a comma and the indication of the sex chromosomes. Thus, 46, XX corresponds to a woman's karyotype; and 46, XY represents a male's karyotype.
At chromosomal alterations Numeric numbers should be indicated after the sex chromosomes, followed by a sign (+ or -) and the affected chromosome. In the case of Down syndrome, as there is an increase in chromosome 21, the formula is 47, XX, +21 or 47, XY, +21. Note that 47 chromosomes are represented in place of the number 46 in the normal human karyotype formula. In the case of monosomy 7, the karyotype must be 45, XX, -7 or 45, XY, -7. When chromosomal alterations affect the sex chromosomes, we can also identify them in the writing of their formulas. An example is Turner syndrome which is represented by 45, X.
→ Importance of karyotyping
Karyotyping is important, as it allows analyzing the karyotypes of individuals and noticing some genetic changes, such as structural and numerical ones. An example is the detection of Down's syndrome, genetic alteration that has three chromosomes 21.
By Ma. Vanessa Sardinha dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/biologia/o-que-e-cariotipo.htm
