Monday, 2 February 2015

Haplotype (PART 1): What's it good for?

Not much.

I kid, but haplotype results are not good for as much as most people initially assume. A common assumption seems to be that the result reflects one half of your ancestry (your maternal or paternal "side") but in fact it represents only a minuscule amount of your overall heritage.

If you made this mistake, don't worry, so has pretty much everyone who ever received results from a commercial testing company. Haplotype results are over-hyped and tend to dominate ancestry DNA reports (for reasons I won't get into here).

With this post and a couple of follow-up blogs covering investigations I am working on, I hope that I can help you navigate through the hype, bringing haplotypes to ground in the area where they are actually useful: using their logical inheritance pattern to prove/disprove theories of relationships for which no documentation can be found.

The simplest way to understand a "haplogroup" is as a grouping of Y-DNA results or mitochondrial DNA results based on shared variants in the 59 million bases in a male's Y chromosome or or 16.6 thousand bases in anyone's mitochondrial DNA. (This is how the term haplogroup is used in genetic genealogy, biologists use it for all sorts of stuff).

Every individual tested who shares the exact same variants at key locations on the relevant chromosome is assigned the same haplotype. They all inherited these variants from ancestral lines that lead back to the same person a very, very long time ago. Likely tens of thousands of years ago, given the resolution of most basic tests (if you've used a high resolution STR marker test you probably already know this stuff so I don't feel bad about making a slight oversimplification about timelines).

Everyone in a group got their variants from the same person many thousands of years ago, and still has the same sequence of variants, because of two simple facts: Y-DNA gets passed down from father to son without recombining, and mitochondrial DNA is the non-nuclear DNA inherent in the egg cell itself (the sperm's mitochondrial DNA does not survive fertilization) so it also passes intact, but from mothers to all of their children. You, your mom, and her mom's mom's mom, etc. in a straight line of maternal relationships, all have the same mtDNA haplotype. There is a small mutation rate, but don't worry about it until you've become more expert in using haplotypes.

So, how does that type define you?

It really doesn't reflect much about your complete genetic make-up.

Categorizing 16.6 thousand base pairs out of a total of 3 billion is categorizing a measly 0.0005% of who you are, genetically. Women don't even have a Y chromosome and for men it is only about 2% of their total genetic make-up. However, as insignificant as these percentages are, these are the only groupings of DNA that can be made to reflect ancient ancestry and follow a specific logical inheritance pattern, because all your other DNA emerged from mixing events every single time one of your ancestors was conceived. So, the fact that these pieces of DNA do not change and are associated with specific people in every ancestry chart is pretty cool and can be a powerful tool in certain investigations.

So, your haplotype does not really define much about your overall genetic identity, does it tell you much about your relationships with genetic matches on autosomal tests?

I'll answer that in PART 2...

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