Identifying Autosomal Ancestors & Autosomal Relatives
Several Direct-to-Citizen (DTC) DNA testing companies offer gene-chip tests that determine the bases present at ~ 1 x 10^6 SNPs, with most of these positions located on one's 22 autosomal chromosome pairs. A comparison of the % shared/identical DNA with other tested individuals allows one (a) to identify autosomal relatives among them and (b) by then comparing one's family trees to identify common autosomal ancestors.
As explained in this document, these comparisons are limited to a genealogical time frame of up to 6 generations ago.
The two figures were obtained from the following two documents written by the two authors: