Females typically have two of the same kind of sex chromosome (XX) and are called the homogametic sex. Males typically have two different kinds of sex chromosomes (XY) and are called the heterogametic sex. – Source Wikipedia
The X chromosome is significantly longer than the Y chromosome and contains hundreds more genes. Because the additional genes in the X chromosome have no counterpart in the Y chromosome, the X genes are dominant. This means that almost any gene on the X, even if it is recessive in the female, will be expressed in males. These are referred to as X-linked genes. Genes found only on the Y chromosome are referred to as Y-linked genes and expressed only in males. Genes on either sex chromosome can be called sex-linked genes.
There are approximately 1,098 X-linked genes, though most of them are not for female anatomical characteristics. In fact, many are linked to disorders such as hemophilia, Duchenne muscular dystrophy, fragile-X syndrome and several others. They are responsible for red-green color blindness, considered the most common genetic disorder and found most often in males. The non-sex feature X-linked genes are also responsible for male pattern baldness.
In contrast to the large X chromosome, the Y chromosome contains only 26 genes. Sixteen of these genes are responsible for cell maintenance. Nine are involved in sperm production, and if some are missing or defective, low sperm counts, or infertility may occur.
Sources: Wikipedia and the Live Science Contributor 12.09.17. – Jessie Szalay
By Annmarie Dallao
ARCpoint Labs of Reading
