The set of pairs of chromosomes that a cell has is called a karyotype.
The concept of karyotype has its origin in two words from the Greek language: káryon , which can be translated as “nucleus” , and týpos (which translates as “type” ). The notion, used in the field of biology , refers to the group of pairs of chromosomes that a cell houses .
The karyotype presents a specific number of chromosomes , with a certain size and a certain 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 non-sexual (autosomal) pairs and one sexual pair .
Karyotype groups
In the human karyotype, seven groups appear, 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 located in a characteristic place in each pair).
The human karyotype, therefore, is composed 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).
With respect to the only sexual pair of chromosomes of the standard human karyotype, mentioned in a previous paragraph, we can say that in the man , it is made up of an X and another Y chromosome ( XY pair), while in the woman it includes two X chromosomes ( pair XX ). If this karyotype is constituted in another way, an abnormality in the development of the individual may be recorded. People with Down syndrome , for example, register trisonomy of the 21st pair : instead of two chromosomes in the 21st pair, they have three.
As an analysis, the karyotype or karyogram requires a blood draw.
The cariogram
In the clinical setting, this term and 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, performing 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 use cells called lipocytes , which can be obtained by drawing blood. Another possibility, if the patient is a pregnant woman, is to take it from the amniotic fluid.
The karyotype allows us to appreciate the diversity of the chromosomes, since all of them are distinguished from the others by their size, shape and by the arrangement of the bands that can be seen along their body. Thanks to the cariogram it is possible to detect various alterations , which may be numerical or structural . One of the most common examples is Down syndrome, whose alteration is numerical and is detailed above.
Different syndromes linked to karyotype alterations
Another known numerical alteration is Klinefelter syndrome , which occurs in men and causes reproductive problems; Precisely, a failure appears in the testicles that usually triggers infertility disorders. In this case, two X and one Y chromosomes are seen.
Turner syndrome , on the other hand, appears in women who have only one X chromosome. The lack of the other means that sexual characteristics cannot be fully developed, which is why the organism is incapable of sexually reproducing.
In structural alterations, some chromosomal regions may be absent or duplicated , and this can lead to various types of consequences, depending on the genes that are compromised.