Archive for November, 2009

The Economist Mangles Disease Genetics

Sunday, November 29th, 2009

The Economist has a rather distressingly bad article by the evolutionary psychologist Geoffrey Miller, about the supposed general failure in human disease genetics over the last 5 years. The thesis is that Genomes Wide Association Studies (GWAS) for common diseases have been a failure that geneticists are trying to keep hidden, and that the new techniques required to solve the problem of disease genetics will raise ‘politically awkward and morally perplexing facts’ about the different traits and evolutionary histories of races. The former claim is pretty much the same as Steve Jones Telegraph article earlier this year, and is just as specious. I will look at both claims separately.

A quick point of terminology: Miller uses ‘GWAS’ to refer to studies that look for disease association in common variants using a genotyping chip, and acts as if sequencing studies are not, in fact, GWAS. In fact, a sequencing association study is just another type of GWAS, just looking at a larger set of variants.
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How Many Ancestors Share Our DNA?

Wednesday, November 11th, 2009

Over at the Genetic Genealogist, Blaine Bettinger has a Q&A post up about the difference between a genetic tree and a genealogical tree. The destinction is that your genealogical tree is the family tree of all your ancestors, but your genetic tree only contains those ancestors that actually left DNA to you. Just by chance, an individual may not leave any DNA to a distance descendant (like a great-great-great-grandchild), and as a result they would not appear on their descendant’s genetic tree, even though they are definitely their genealogical ancestor.

At the end of his post, Blaine asks a couple of questions that he would like to be able to answer in the future;

  • At 10 generations, I have approximately 1024 ancestors (although I know there is some overlap). How many of these ancestors are part of my Genetic Tree? Is it a very small number? A surprisingly large number?
  • What percentage, on average, of an individual’s genealogical tree at X generations is part of their genetic tree?

I think that I can answer those questions, or at least predict what the answers will be, using what we already know about sexual reproduction.
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