X Chromosome: Sex chromosome present in both sexes, of species in which the male is the heterogametic sex
The X chromosome is one of the two sex chromosomes in mammals.
They decide the sex (gender) of an individual. The other sex chromosome is the Y chromosome.
Females have two X chromosomes, males have one X and one Y. An egg always carries a single X, while sperms carry either an X or a Y. That is how sex is determined in humans, and in most other mammals. Although females have two X chromosomes, each cell can only have one X chromosome active. During early development, a process called X-inactivation occurs. In each cell one of the X chromosomes randomly deactivates. This causes different parts of the body to have different X-linked genes, and is responsible for the black and orange coloration of calico cats.
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