What is a chromosome?
The chromosomes are small complex structures shaped strand found in the cytoplasm of the nucleus of the cells of all living beings lose . These filaments undergo duplication and separation during somatic cell division (mitosis) and the special cell division that results in the formation of gametes (meiosis).
They are composed of chromatin that is 35 percent deoxyribonucleic acid (DNA), 10 percent ribonucleic acid (RNA), 35 percent histone proteins, and 20 percent non- histone.
The pairs from 1 to 22 are the same in both women and men; these are the autosomal ones. But pair 23 is the one that accounts for sex and has the fusion XX in the case of women and XY in the case of men; they are the sex chromosomes .
There are types of these tiny bodies. It can be said that they are divided into two groups:
-Procariotics: they are composed of a single DNA chain and are located in the nucloid. They are circular DNA strands that are bound to the cell membrane . They have plasmid that probably combines with the main DNA. They are also found in eukaryotes within other organelles such as chloroplasts and mitochondria.
-Eukaryotic: formed by a single chain of linear DNA in which the DNA molecule is captured by histone proteins and they are found in the inner part of the nucleus in the form of a network, which causes that during cell division they generate the various types .
-Depending on the location of the centromere (part of the chromosome that divides the two arms where the two chromatids meet) they can be:
- Metacentric (Fig. D): it is located in the middle of the structure and the two arms measure the same
- Submetacentric (Fig. C): it is displaced and the length of one of the arms is slightly greater than the other.
- Telocentric (Fig. A): only one arm can be seen since the centromere is at the end. They do not occur in the cells of the human species.
- Acrocentric (Fig. B): Also located at one end with a large arm relative to the other.
-Homologists: they exert a crossover with each other during meiosis cell division . They usually have the same DNA sequence from one end to the other, therefore, they carry the same genetic information. They are those pairs of chromosomes that are inherited from the parents: one from the mother and the other from the father, whose genetic contents are alleles, auxiliary forms of the same gene that locate the same space.
-Somatic: they are all those who are not sexual . As mentioned before, they are pairs 1 to 22 of human chromosomes.
-Heterochromosomes: are those that contain sexual information. They are used to determine the sex of a human being: it is female if a pair of X chromosomes is joined and it is male if an X and a Y chromosome are joined.