Please see the Sorenson Molecular Genealogy Foundation website. It can be found by doing a search under SMGF.
They are doing free genealogy testing for the Y and mitochondrial DNA. I have a brickwall after my great grandfather, John Clark(e)Tomlin whose names might have originally been Tomerlin. The 1880 census of MOntgomery County, Alabama shows he was born about 1857 in Georgia to a North Carolina born father and a Georgia born mother. He married Roxie Catherine Jackson in 1879 and they had one child, Roy Laitten Tomlin. John died when Roy was a small boy.