Karyotyping

 

Karyotype is a complete chromosome set reflecting the entire set of characteristics inherent in this biological species (individual karyotype). The human body can undergo mutations and changes, but the karyotype will remain unchanged, so there is no need to re-examine.

A human karyotype contains 23 pairs of chromosomes, of which 22 are autosomes, that is, the same for female and male organisms, while the 23rd pair is responsible for sex differences. For women, the homogametic chromosome set (identical sex chromosomes) is XX, and for men, the different one XY. Such a chromosome set is not typical for all living beings. Among some species of insects, fish and birds, female persons have XY chromosomes, and male ones have XX. In the absence of pathologies of the karyotype, the female is written by the formula 46XX, and the male 46XY.

What are the purposes for conducting karyotyping?

Usually, there must be certain reason for running karyotype test. Karyotyping is necessary for:

• Detection of chromosomal mutations to prevent the birth of a child with chromosomal abnormalities.

• To diagnose the causes of miscarriage.

• If there are signs of genetic abnormalities in children.

• With a history of genetic abnormalities among blood relatives.

• If a pregnant woman is at risk of invasive prenatal diagnosis.

How is the research done?

To carry out this analysis blood cells of the peripheral system are used. Most often, lymphocytes are used in the active division stage. Outside this stage, the analysis of the DNA molecule in a light microscope is technically not possible.

To systematize the karyotype, chromosomes are photographed, analyzed and numbered. It is customary to orientate the images vertically and number them in descending order of size. Last place is taken by a pair of sex chromosomes.

What are the consequences of deviations from the norm in the karyotype?

Changes in the karyotype in humans in most cases speak of developmental defects that entail severe, often incompatible with life, diseases. Such anomalies most often lead to spontaneous abortions in the early stages. Only about 3% of pregnancies with karyotype abnormalities end with a birth.

There are such karyotypic anomalies as:

  • trisomy - the presence of three chromosomes instead of two. Such a gene mutation causes the syndromes of Klinefelter, Down, Edwards, Patau.
  • monosomy - the absence of a diploid organism of chromosomes in a pair (Shereshevsky – Turner syndrome).
  • deletion - lack of part of the chromosome. For example, one of the causes of male infertility may be the loss of the site in the Y chromosome.
  • duplication - duplication or change of the chromosome structure.
  • inversion - a partial reversal of the chromosome.
  • translocation - rearrangement of chromosome regions in the chromosome pair.

It is within the competence of the geneticist to make conclusions, give comments and predictions on the results of the research.

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