Prepared by Elisabeth Lindsay.
The X chromosome is one of the chromosomes that determine gender, the other being the Y chromosome. Females have two X chromosomes, where males have one X and one Y chromosome. Females pass one X chromosome along to each child, male or female; while males pass a copy of their X chromosome along to their daughters, but not their sons. Female X chromosomes. like autosomal chromosomes, undergo recombination, but the male X chromosome does not. And like autosomal DNA, X chromosome DNA is informative for both recent and deep ancestry; although the X-DNA test is not as well-known as Y-DNA and autosomal DNA tests. DNA studies, in general, are highly useful, if not precise genealogical tools, enlightening research and helping researchers connect with others.
For more information on DNA studies and their uses in genealogy, see the GenWeekly articles, Beyond the Paper Trail: Discovering Family History with Different DNA Tests ($) and SNPs and Snails: What is your deep ancestry? ($).