Repressive heterochromatin, which compresses the DNA and inhibits certain genes from expressing, silences the deactivated X-chromosome. This means that each cell in the body of both sexes contains precisely a single functional and usable copy of the X chromosome. One of several X chromosomes become spontaneously and permanently partially deactivated in cells apart from egg cells, in the early phase of the female development of embryo: in certain cells, the X chromosome which is inherited from the (female)mother tends to be disabled, whereas, in other, the X chromosome which is inherited from the male (father) is deactivated. Throughout the ovum, the X chromosome is often identified as the 23rd chromosome, whereas a particular sperm can have perhaps an X or a Y chromosome. Pseudoautosomal regions are small homologous regions mostly on X and Y chromosomes. Females possess 23 pairs of homologous chromosomes, whereas males have 22 pairs.
These are homologous chromosomes, meaning that they have the very same genes (DNA regions) in much the same sequence in their chromosomal sides.Īllosomes are the chromosomes of the 23rd pair, which in most females have two X chromosomes and most males have an X chromosome and a Y chromosome. Autosomes are the first 22 pairs of chromosomes. The answer to the question ‘how many sex chromosomes does humans have’ is that each nucleus of a human cell comprises 23 chromosomes pair, for a total of 46.