Humans have 23 pair of chromosomes (in total 46). Out of these 23 pairs, 22 pairs are numbered chromosomes called autosomes and 1 pair is the sex chromosomes.
The autosomes look same in males and females whereas for sex chromosomes, males have XY chromosomes whereas women have XX chromosomes. Human X chromosome is around three times larger than the Y chromosome; X chromosome contains around 99 genes whereas Y chromosome have around 55 genes.
In a pair of chromosomes, each chromosome is inherited from one parent. This implies that we get one half of our chromosomes from our mother and the other half from our father.
The number of chromosomes is the same in all human cells except for the sex cells (female eggs and the male sperms); these cells contain half the number of chromosomes (23 chromosomes).
Any change in the structure or number of X chromosomes can lead to a number of genetic diseases.
Some women may inherit only one copy of the X chromosome, which causes Turner syndrome. Sometimes, there are three X chromosomes instead of two, leading to trisomy X syndrome.