a genealogist's sketchbook

The last time I blogged this we had just received preliminary data from a fourth member of our family to be tested, a cousin whose data pushes the ‘common ancestor’ back to Simon² Taylor, who died in 1729. Now more of this cousin’s data are available, yielding the following data table:

This raises some interesting questions about interpreting DNA data. Judging only from the discrepancies in loci 34 and 35, the first and second subjects look more closely related, and the third and fourth also. Following the pedigree chart in my last Taylor DNA post shows that this is true for the first pair, but not for the latter pair: the third subject is more closely related to the first two, than to the fourth subject. The fact that nos. 1 and 2 share a common ancestor whose father was the ancestor of 3, and whose grandfather was the ancestor of 4, suggests that the values held by 3 and 4 in those loci are the original values, and that the common ancestor of nos. 1 and 2, Harrison Taylor, was the man who had a spontaneous mutation in both loci, 34 and 35. This is based on the assumptions that (1) the people in this DNA sample are related in the way they are shown to be by the traditional genealogcial evidence; and (2) when two people with a known common ancestor share a particular DNA STR value in a given genetic locus, then their common ancestor also had that value, since the probability of two identical mutations occurring in near cousins is statistically insignificant. Unless one of these assumptions is wrong, then we conclude that the third and fourth subjects determine the ‘original’ values for their common ancestor, Simon² Taylor; and furthermore only locus 9, out of the first 37, remains ambiguous for the common ancestor, Simon² Taylor (1667/70 – 1729). We are in the process of collecting more detailed data, to build an unambiguous 67-marker profile for Simon² Taylor. This chart might help:

To test this theory (that Harrison⁴ Taylor is the originator of mutations in both loci 34 and 35), hopefully we can secure samples from a descendant of another of Harrison’s sons, as well as from the descendant of Septimus³, brother of George³ and John³, who has already agreed to a test. So there is more to come!