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Chromosome analysis

CHROMOSOMAL ANALYSIS: What valuable information does the karyotype provide?

What does the word "karyotype" mean?

A karyotype (from the Greek. Karyon - nut and typos - imprint, shape) is a combination of characteristics of chromosomes in number, structure, shape, etc. .. Different species have different numbers of chromosomes. As you know, a person has 46 chromosomes: 44 autosomes (not determining sex) and 2 sex chromosomes. Accordingly, the normal karyotype of a man is designated as 46, XY, and women - 46, XX.

46,XY- нормальный мужской кариотип, анализ проведен с применением стандартных методов цитогенетики

46, XY - normal male karyotype, analysis was carried out using standard methods of cytogenetics

 

 NOR - хромосомный анализ с применением молекулярно-цитогенетического метода FISH

NOR - chromosome analysis using the molecular cytogenetic method FISH

What is a chromosome?

Chromosome (from the Greek. Chroma - color and soma - body) - a complex of DNA molecules with proteins. Human DNA, if you stretch the thread, reaches a length of about two meters. In order to compress the hereditary material in size, nature provides for the compactization of a DNA molecule in several stages. As a result, a typical human cell nucleus, observed only with a microscope, occupies a volume of about 110 μm³, and the human chromosome on average does not exceed 5 - 6 μm. On each chromosome, one DNA molecule with a unique sequence is compactly packed. Such organization of the genetic material is necessary so that the separation of DNA is equivalent between the cells of the body or the germ cells that are formed for conception.

Why is karyotype analysis important?

The set of chromosomes normally corresponds to certain quantitative and structural criteria that experts evaluate. In humans, as mentioned earlier, 46 chromosomes correspond to the normal number. But at the same time, structural disturbances in the structure of chromosomes are possible. If these are balanced rearrangements - translocation (exchange of sites of different chromosomes) or inversions (rearrangements within the same chromosome), then this will not affect the health of the carrier. At the same time, if in a married couple one of the spouses is a carrier of perestroika, then there are often cases of spontaneous miscarriages or the birth of children with developmental defects. Other features of the chromosomes that are considered normal variants can cause an incorrect quantitative distribution of chromosomes in germ cells, and this leads to the formation of an embryo with a chromosome deficiency (for example, monosomy X - Sherishevsky-Turner syndrome) or with an extra chromosome (for example, trisomy 21 - syndrome Down).

If a person has 46 chromosomes, then how can they be distinguished?

All chromosomes vary in size, structure and shape. Each chromosome has its own pair, since one chromosome from the pair we get the mother from the egg, and the second similar father from the sperm.

Depending on the size, scientists numbered each pair of chromosomes from large to smaller. Each pair of chromosomes also has its own individual sequence of active and inactive zones. In order to see this striation, employees of cytogenetic laboratories perform various manipulations and apply different methods of staining the drugs.

What do you need to know your karyotype?

Chromosomal analysis can be carried out using various biological material: blood lymphocytes, bone marrow, abortion material, amniotic fluid cells, placenta, and even early embryo cells before transferring them to the uterine cavity. What material will be taken for research depends on the tasks and the reasons for the analysis. Most often, a human karyotype is established by culturing lymphatic cells of venous blood. At the same time, a small amount of blood is placed in a nutrient medium for 72 hours at a temperature of 37 ° C. Since chromosomes can be seen only at a certain stage of cell division (metaphase stage), a special reagent is added to the cell culture, which stops the process of division precisely during the metaphase. Next, the cell culture undergoes a fixation process, after which the preparation for analysis is underway. From the moment of receiving blood to receiving the finished product suitable for research, on average, two weeks pass, and the patient receives the result of the analysis in a month.

How is the analysis of drugs?

As soon as the preparations have passed all the necessary stages of preparation, they are sent for analysis to a specialist cytogenetics. Using a special program, a specialist arranges all the chromosomes according to their numbers, and then checks each strip on each chromosome with a generally accepted scheme called an ideogram. In this case, 15-20 cells are analyzed. Therefore, the study of each patient takes about 6 hours.

What is the peculiarity of the analysis of the karyotype in the Medical Center of the IGR?

The diagnostic laboratory for its work uses only high-quality reagents of European and American production. The quality of the preparations meets the requirements of the European Association of Cytogenetics (E.C.A.), and the study is carried out in accordance with the international nomenclature ISCN (An International System for Human Cytogenetic Nomenclature). To analyze the preparations of each patient, not only standard cytogenetics methods are used (for example, staining of drugs with G and C methods), as well as molecular cytogenetic diagnostic methods (FISH - in situ fluorescence hybridization). Such an integrated approach allows you to accurately establish all the possible options and features of the karyotype.

How is it prepared before donating blood for a karyotype?

Blood is taken from a vein.

Not on an empty stomach! A desirable condition is the lack of antibiotic therapy, recent x-ray studies, drinking alcohol on the eve and elevated body temperature. These factors negatively affect the growth of cell culture, as a result of which there may be a need for re-sampling of the material.

Studies are performed over 4 weeks.

You can get the results at the reception of the medical center.

Whatever the result of the karyotype, the doctors of our center will hold a qualified consultation and offer all possible options so that happiness comes to your family.