About Site Map Contact Us |A service of the U.S. National
Library of Medicine®| Reviewed January 2010 What is the Y
chromosome? 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 more than 59 million building blocks of DNA
(base pairs) 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 50 to
60 genes that provide instructions for making proteins. Because
only males have the Y chromosome, the genes on this chromosome
tend to be involved in male