Genetic genealogy complements traditional family history research by confirming — or disproving — ancestral relationships. The most popular test, Y-DNA, examines genetic “markers” on a man's Y chromosome. Because the Y chromosome changes little (if at all) as it's passed from father to son, men know they're related if their Y-DNA matches.
Here's an example: James Zavacky and Peter Zavatsky want to find out whether they're related, so each takes a 25-marker Y-DNA test. In comparing their results, they discover that 24 of those 25 markers are identical, with a mutation at marker 449:
