The free online searchable genetic database offered by the Sorenson Molecular Genealogy Foundation has added mtDNA data from more than 4,000 individuals. This is an expansion on its more than 15,000 individual genetic profiles based on Y-chromosome (paternal line) testing. Unlike Y-chromosome DNA, which is only passed down the male line from father to son, mitochondrial DNA (mtDNA) is inherited by both men and women from their mothers, making it a useful tool for tracing maternal ancestry. The free genetic database allows you to search by surname (Y-chromosome only) or by your genetic marker profile from any testing lab to bring up matching bring DNA profiles and linked genealogies. More mtDNA profiles will be added as they can be processed, probably 1,000 to 2000 per month, the foundation says.

More About Genetic Genealogy:
Genetic Basics - Making Sense of Markers & Mutations
Tracing Your Ancestry Through DNA