Y-DNA Overlay Chart -- GLASTONBURY line

A new type of DNA chart introduced in Second Site presents data in a more intuitive viewing format than the usual grid. Below you'll find abbreviated DNA signatures overlaid on a familiar descendant chart constructed with traditional genealogical ("paper") evidence. This overlay chart includes calculated Y-DNA signatures for ancestors derived from the test results of their descendants. 

For the MRCA (Most Recent Common Ancestor), a derived signature is often called a modal signature. This DNA Overlay Chart, however, does not derive DNA signatures using the statistical mode — i.e., it does not choose the values that occur the most frequently in the set of descendant markers. Instead, it uses a "maximum parsimony" method described by Alvy Ray Smith. The rules are designed to choose marker values that would produce the observed test results of descendants via the minimum number of mutations.

The Second Site program which built this chart derives probable DNA signatures. It is possible for unlikely mutation sequences to occur, such as multiple mutations occurring in the same generation, which obscure the DNA signature of the father. All methods for deriving DNA signatures are subject to uncertainty, but the maximum parsimony method reduces the possibility that a bias in the test results (many people tested from one branch of the family) will unduly influence the derived DNA signature of the MRCA.