Sex Chromosomes

Mechanisms involved in the origin and maintenance of large non-recombination regions on sex chromosomes have been mainly studied in plants and animals, but similar features have recently been found in fungal chromosomes carrying zygotic genes in some species It was conscious. Phenomenon (Fraser et al., 2004). Plant and animal sex chromosomes have evolved from an autosomal pair by elongation of non-recombination regions surrounding complementary genes that define sex-specific function (Bergero and Charlesworth 2009).

Humans have another pair of sex chromosomes with a total of 46 chromosomes. Sex chromosomes are called X and Y, and their combination determines the sex of a person. Typically, a human female has two X chromosomes and a male has an XY pair. This XY sex determination system exists in most mammals, as well as several reptiles and plants. When a sperm fertilizes an egg, it is determined whether the person has XX or XY chromosome. Unlike other cells in the body, the egg and sperm cells (called gametes or sex cells) have only one chromosome. Gametes are produced by meiotic cell division, which disrupts cells with half the number of chromosomes as parent or progenitor cells. In the case of humans, this means that the parent cell has two chromosomes and the gametes have one chromosome.

The X chromosome is one of two human sex chromosomes (the other is the Y chromosome). The sex chromosome constitutes one of 23 pairs of human chromosomes in each cell. The X chromosome spans approximately 155 million DNA components (base pairs), accounting for about 5% of the total DNA of the cell. Everyone usually has a pair of sex chromosomes in each cell. Females have two X chromosomes, and men have one X chromosome and one Y chromosome. In the early stages of female embryogenesis, one of the two X chromosomes is randomly and permanently inactivated in cells other than the egg cells. This phenomenon is called X deactivation or ionization. X inactivation ensures that women, such as men, have a functional copy of the X chromosome in each somatic cell. As X inactivation is random, in normal women, the X chromosome inherited from the mother is active in several cells and the X chromosome inherited from the father is active in other cells.