25 August 2015

How much DNA do you inherit from your grandparents?

This re-post on FB of a Slate post could not have come at a better time! The associated image alone speaks to a main takeaway point from my weekend.

On Saturday while visiting the delightful Augusta Genealogical Society, besides giving three talks on NC research, I gave one talk on the basics of DNA testing for genealogy.

One point I made is that due to the nature of genetics, we don’t get exactly 25% from each grandparent and as you go back in time, you might find that you have large bits of genetic material from one branch of your family tree and practically none from another, regardless of what the basic math suggests on the surface (e.g. 50% from each parent who received 50% from each of their parents, etc)! It is very important to appreciate this when considering autosomal testing.

Well, Which Grandparent Are You Most Related to? pursues this concept in some depth based on extensive personal DNA testing in his own family along with the supporting genetics math about how we disproportionately inherit.  Though I don’t necessarily agree with the author’s intended use of what he is learning as a geneticist, the point that we don’t inherit equally from  grandparents and succeeding generations, is what I want to emphasize.

Related to this, Upfront with NGS recently blogged about In the future ... we might be able to reconstruct what our ancestors looked like! that is based on using DNA data to reconstruct what ancestors may have looked like.  A component of this at the individual level is understanding the correlation of DNA to various features along with the recognition that we did not inherit precise percentages of genetic material from all the ancestors of any one generation in our tree. 

Some of us look like the spitting image of maternal great aunt Lucy while a sibling might look like paternal uncle Alfred.  We know we are siblings and yet genetic inheritance clearly has endowed us with dominant bits from different branches of our family tree.  Something to keep in mind as you do DNA testing, start processing your test results and correlate them with test family members, photos of the deceased and more.

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