The concept of karyotype has its origin in two words in the Greek language: káryon, which can be translated as “nucleus”, and týpos (whose translation is “type”). The notion, used in the field of biology, refers to the group of pairs of chromosomes that a cell houses.
The karyotype has a specific number of chromosomes, with a certain size and shape, which is linked to the characteristics of a species. In the case of humans, the species generally has 23 pairs of chromosomes: that is, 46 chromosomes in total in the nucleus of a cell. The organization of the human karyotype develops into 22 pairs that are not sexual (autosomal) and one sexual pair.
Seven groups appear in the karyotype of the human being, each identified with a letter. These sets are formed according to the position and length of the centromere (a region of the chromosome that is found in a characteristic place in each pair).
The human karyotype, therefore, is made up of Group A (the chromosomes of pairs 1, 2 and 3, which are the largest), Group B (pairs 4 and 5, also large in size), Group C (pairs 6 to 12 and the sexual pair), Group D (pairs 13, 14 and 15), Group E (pairs 16, 17 and 18), Group F (pairs 19 and 20) and Group G (pairs 21 and 22).
Regarding the only sexual pair of chromosomes of the human standard karyotype, mentioned in a previous paragraph, we can say that in men, it is made up of an X and a Y chromosome (XY pair), while in women it includes two X chromosomes (par XX). If this karyotype is constituted in another way, an abnormality in the development of the individual may be registered. The people with Down syndrome, for example, record the trisonomía of the pair 21: instead of two chromosomes in pair 21, have three.
In the clinical field, this term and the karyogram are often used interchangeably to refer to the latter, which is a chromosomal analysis of cells with the purpose of detecting certain acquired and congenital diseases. In the case of people who wish to resort to assisted reproduction, for example, this test is of great importance, especially if there is ovarian failure, seminal alteration or abortions.
To carry out a karyogram it is necessary to make use of cells called lipocytes, which can be obtained through a blood draw. Another possibility, if the patient is a pregnant woman, is to take it from amniotic fluid.
The karyotype allows us to appreciate the diversity of the chromosomes, since all are distinguished from the others by their size, shape and by the arrangement of the bands that are noticed throughout their body. Thanks to the karyogram, it is possible to detect various alterations, which can be numerical or structural. One of the most common examples is Down syndrome, the alteration of which is numerical and is detailed above.
Another known numerical alteration is Klinefelter syndrome, which occurs in men and causes reproductive problems; precisely, there is a failure in the testicles that usually triggers infertility disorders. In this case, two X and one Y chromosomes are noticed.
The Turner syndrome, on the other hand, appears in women who have only one X chromosome Lack of other causes can not fully develop sexual characters, which is why the body is unable to reproduce sexually.
In structural alterations, some chromosomal regions may be absent or duplicated, and this may have various types of consequences, depending on the genes that are compromised.