DNA testing works in many ways and it is the Y-DNA testing that is referred to on this information page.
In simple terms, when the 23 pairs of chromosomes from the woman and the 23 pairs of chromosomes from the man get together, a baby is made. The egg always carries the "X" chromosome and the sperm carries either the "X" or the "Y" chromosome. If a "Y" sperm fertilises the egg, a boy is produced ("X-Y") but if an "X" sperm fertilises an egg, a girl is produced ("X-X").
The "Y" chromosome therefore gets passed down from generation to generation via the male side of the family and it is the analysis of specific points of the male DNA that can determine if there is a common link between two unrelated men, even if the link is several generations back.
Get Yourself DNA Tested
Should anyone else wish to get themselves tested, please visit Family Tree DNA where there is already a Surname Project for the Leeds'.