A chromosome it is a condensed structure of DNA (deoxyribonucleic acid) present in the cells that appears in constant number in each plant or animal species. Chromosomes store much of the Genetic information .
The shape of the chromosomes varies according to the cellular stage. While in the interface it is impossible to visualize them with an optical microscope, in the meiosis wave mitosis acquire the structure of X Which is better known.
The specific appearance of each chromosome is given by the centromere , a region that, subject to staining, is less stained than the other parts of the structure. The ends of the chromosome, meanwhile, are called telomeres . Each chromosome has a particular position of the centromere and a certain length, and from each of them there is another identical one. This means that the homologous chromosomes form peers (there are two equal chromosomes).
Homologous chromosomes have the same genes located in the same sites (known as locus ). In those organisms that reproduce sexually, one of the chromosome pairs is contributed by the mother and the other for the father . Thus, each diploid organism has two copies of each gen .
In the case of human being , the constant number of chromosomes of the species is 46 , since each individual presents 23 pairs of homologous chromosomes . Of these 23 peers, 22 belong to somatic chromosomes and the rest, to sex chromosomes (XX in women and XY in men).
When a disturbance of these constants, a genetic disorder is generated. He Down's Syndrome , for example, develops when there is an additional copy of the chromosome 21 : In this case, there are three chromosomes instead of two.
The so-called chromosomal diseases they arise from anomalies in the chromosomes, being the alteration of the amount of sex chromosomes the most common of all. The symptoms and consequences of these disorders They are very serious, since they usually cause abortions, mental retardation and congenital malformations.
In broad strokes, it is possible to group chromosome anomalies into two large groups: those of the number and those of the structure.
Chromosomal number anomalies
During sexual reproduction, the father and mother each contribute 23 chromosomes that bind and give rise to the 46 that we must have in our material genetic to enjoy good health and go through proper development. Depending on the point of pregnancy at which the anomaly occurs, the characteristics are different.
If the anomalies occur during meiotic division or fertilization, then they are called homogeneous . This division is also known as meiosis and it is the process by which gametes are created; if something out of the ordinary happens at this time, then the anomaly will affect the rest of the zygote cells during the fertilization .
Chromosomal abnormalities of the structure
This type of anomalies occurs less frequently than those of number; However, since they may go unnoticed due to lack of visible symptoms or effects, the percentage of the population affected is not known very precisely.
One of the most common forms of anomaly of the structure is the deletion , which is that part of the chromosomal material is lost, something that is associated with the Wolf-Hirschhorn syndrome and that of cat meow .
It is called translocations , on the other hand, to the exchange of genetic material that takes place between two chromosomes or more. The investments they are alterations that harm a chromosome when it suffers a break and its arms are reversed; is pericentral if you invest a fragment that includes the centromere, and paracentral In the opposite case.