FAQ Regarding DNA
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Frequently Asked Questions (FAQ) Regarding the Lindsay Surname DNA Project

1. Question: If two men have a Y-chromosome match on 25 of 26 markers, but there is a two step difference on one marker, is that considered one or two mutations?  Answer: Currently it is perceived that most microsatellite marker mutations appear to be single-steps, but there are rare cases (about 1/30 - 1/50) of two-step mutations.  With the current level of genetic thinking, it is not possible to interpret this knowledge at this time with any degree of certainty, but according to Dr. Bruce Walsh, geneticist at the University of Arizona, if all the other markers match between the two individuals, you can treat a two step mutation as a single mutation event.  If there are multiple marker mismatches (three or more) that implies that the Most Recent Common Ancestor (MRCA) lived so long ago that there has been time for two independent mutations at that one marker.  Dr. Walsh has more background information and a lookup table where you can check the effect if you count the two step mutation as one mutation or two.  This additional information is found at   http://nitro.biosci.arizona.edu/ftdna/tmrca.html

2. Question: How do we arrive at the mutation rate assumption (.002 or .004) for our genealogical DNA studies?  Answer: It is very likely that each of the Y-chromosome microsatellite markers have different mutation rates. Since the current database of specific marker information is so small statistically, we are required to assume a standard mutation rate for all microsatellite markers until such time reliable individual mutation rates can be constructed for each marker.  Currently the most accepted or standard rate is 1/500 = 0.002 which is the average pedigree rate across three significant reported studies--Heyer et al (1997), Bianchi et al (1998), and Kayser et al (2000).  Some researchers choose to use a higher mutation rate of 1/250 = 0.004 which is considered by most geneticists as likely to underestimate (too short) the true times for the most recent common ancestor.  This higher mutation rate is based on the reported study of Holtkemper et al (2001).