GLOSSARY: X Chromosome

An X Chromosome is defined as a sex chromosome that usually occurs paired in each female cell and single in each male cell. The sex chromosomes X X are one of the 23 homologous pairs of chromosomes in a female. The X chromosome spans more than 153 million base pairs (the building material of DNA) and represents about 5% of the total DNA in women's cells, 2.5% in men's.