The Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents almost 2 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. The Y chromosome is present in males, who have one X and one Y chromosome, while females have two X chromosomes.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The Y chromosome likely contains between 70 and 200 genes. Because only males have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and development. Sex is determined by the SRY gene, which is responsible for the development of a fetus into a male. Other genes on the Y chromosome are important for male fertility.

Many genes are unique to the X or Y chromosome, but genes in an area known as the pseudoautosomal region are present on both chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal region are essential for normal development.

Genes on the Y chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.