There's been a lot of hype about DNA testing to help locate ancestors, but how far does it show your connections?
There are several types of DNA testing:
Y-DNA (traces father's line, father's father etc along the male line) timeline around 338,000 years
MtDNA - Female line - timeline around 200,000
Autosomal DNA - timeline around 7 generations (mostly used to connect with living relatives)
Ancestry.com, Family Tree and 23andMe as well as a few others, uses AutosomalDNA which can confirm relationships up to 2nd cousin level. The more family members tested (start with oldest first) the more accurate the findings will be.
Note: According to Ancestry.com farther than seven generations back are unlikely to have passed on more than 1% of their DNA to you. Read more here
