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1,879 bytes added, 16:18, 16 September 2009
Y-line research
The less differences, the more related a person is to the person of which the profile is investigated.
=== Y-DNA Haplogroups ===
Less specific than STR markers, a haplogroup is defined by certain SNP mutations that occur infrequently. It is less useful for estimating degrees of relationship between individuals but useful in a broader way, since it deals with whole populations. A Y-DNA haplogroup will be the same for every male in the direct paternal line (father, father of father, father of father of father, etc), except when a "non-paternal event" occurs (i.e. there isn't a genetic contribution from the legal and recognised father).
One way to use this information in a genealogy program is to allow one to stipulate the haplogroup (I2, R1b, J1a1, etc.) for an individual, and cascade that change upwards through the male line. Then allow for a way to break this chain, possibly marking the fact with a flag or visual cue.
An example: a researcher tests for Y-DNA haplogroup and gets the result as R1b1. It fills the "Y-DNA Hg" attribute with "R1b1" and it is cascaded upwords (and downwards) through all the relevant lines. Donwards doesn't only apply to direct progeny: all the cousins that descend though a paternal line from a common ancestor should also be marked R1b1.
Six months latter a cousin (which should be R1b1) makes the same test and gets haplogroup J2. The initial assertion is clearly wrong, and going upwards the genealogy software could pinpoint the most recent male ancestor and flag the discrepancy. This isn't limited to this kind of situations: we now have the haplogroup of several individuals deceased a long time ago, so this "most remote ancestor" could be in the 16th century.
The relevance of this method is not limited to finding mismatches: the much more common situation is that different tests from different lines will yeld the same result. It even allows one to have a good idea of a certain person haplogroup without making a test.
==M-line research==

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