The karyotype is characteristic of each species, as is the number of chromosomes. Humans have 46 chromosomes (23 pairs because we are diploid or 2n) in the nucleus of each cell, organized in 22 autosomal pairs and 1 sexual pair (XY male and XX female). The autosomes or chromosomes Somatic are classified into seven groups:
- Group A: Formed by pairs 1, 2 and 3, very large chromosomes, 1 and 3 are metacentric and 2, submetacentric.
- Group B: Formed by pairs 4 and 5, large submetacentric chromosomes.
- Group C: Formed by pairs 6, 7, 8, 9, 10, 11 and 12, medium submetacentric chromosomes .
- Group D: Formed by pairs 13, 14 and 15, acrocentric medium chromosomes with satellite.
- Group E: Formed by pairs 16, 17 and 18. Small metacentric chromosome 16 and submetacentric, 17 and 18.
- Group F: Formed by pairs 19 and 20. Small metacentric chromosomes .
- Group G: made up of pairs 21 and 22. Small acrocentric chromosomes .
The pair 23, the sex chromosomes, consists of a chromosome X, metacentric medium, like those of group C, and a Y chromosome, acrocéntrico small, similar to those of the group G.
Through the study of the karyotype, abnormalities in the shape and number of chromosomes can be detected, which can confirm some congenital diseases. In the fetus, the cells obtained by amniocentesis, obtaining cells from the amniotic fluid, or directly from the blood of the umbilical cord.