Cytogenetics is an independentsection of the doctrine of heredity, which explores various, primarily observable (explicated) carriers that contain information about genetic heredity. Such carriers are chromosomes of various types (polytene, mitotic and meiotic), plastids, interphase nuclei, and, to the least extent, mitochondria.
Proceeding from this, the cytogenetic methodis a set of methods and technologies for studying, first of all, chromosomes, during which their quantitative parameter is established, their chemical-biological description is made, the structure and behavior regimes during cell division are investigated. The scientific task of this study is to establish a connection between the character and the dynamics of changes in the structure of chromosomes and the picture that reflects the variability of the characters.
One of the most important areas of research,which involves a cytogenetic method, is the analysis of a human karyotype. This study, as a rule, is carried out on cultures in which the division of sexual and somatic cells occurs.
The most common culture for this kind ofResearch - peripheral blood cells, such as lymphocytes, fibroblasts and bone marrow cells. The most accessible culture used in medical cytogenetics are blood lymphocytes. The reason for this is that, as a rule, they are the subject of analysis in the postnatal period. In the analysis of fetal karyotype, the cytogenetic method involves the use of cell cultures, the choice of which is due to a number of factors. The main of them is the period of pregnancy. For example, with this period of less than 12 weeks, cytogenetic analysis of chromosomes is best performed with the participation of chorion cells, and at gestation periods of more than 12 weeks, it is advisable to examine the cells of the fetus for research. For this purpose, they are specifically isolated from the placenta and fetal blood.
To establish a karyotype, the cytogenetic methodthe study of heredity requires the receipt of a blood sample in an amount of at least 1-2 ml. In this case, the method itself involves conducting a study consisting of three main stages:
- isolation and cultivation of cells on which the analysis will be performed;
- color of the preparation;
- conducting a thorough analysis of the drug under a microscope.
Effective cytogenetic method of genetics canbe only when the following conditions are met. First, there must be a certain number of cells in the metaphase stage. Secondly, cultivation should be carried out in strict accordance with the established rules and for a period of not less than 72 hours. Thirdly, the fixation of cells should be made with a solution of acetic acid and methanol in a strict ratio of these substances 3: 1.
At the stage of drug coloring for cytogeneticstudy the choice of colors is made taking into account the very purpose of the study, that is, what type of restructuring should be studied. Most often, the method of continuous staining is used, since it is most simple to determine the quantitative parameter of chromosomes. Modern studies most often apply this staining method to determine karyotype anomalies in their quantitative expression. But this cytogenetic method does not make it possible to determine and reveal the structural dynamics of chromosomes. Therefore, other, special methods are used, which make it possible to level out this drawback of the method of continuous dyeing. The most common of them, such as the method of differentiated color, G-method, R-method and others.
And finally, the third phase of the study consists inmicroscopic study of stained chromosomes that are in the metaphase stage. During it, the number of normal and abnormal in its condition cells of the human fetal body is established. For this, as a rule, several tissues are analyzed.
