Inferring relatedness

Published on March 31, 2016   25 min

Other Talks in the Series: Statistical Genetics

EMMANUELLE GENIN: Hello my name is Emmanuelle Genin. I work in Brest in the southwest of France, and today I am going to talk about the inference of relatedness.
So, first of all, we need to define what is meant by relatedness. Relatedness defines the fact that individuals are related. And two individuals are related if they share at least one common ancestor. To illustrate, let us consider the three-generation genealogy of Jack and Chloe. So Jack and Chloe are related. They are, in fact, first cousins. And their fathers, James and Albert, are brothers so they are also related. They have two common ancestors, their grandparents, Robert and Mary.
Relatedness has some genetic consequence in terms of allele sharing. Indeed, coming back to the special case of Jack and Chloe and considering a given position on their genome, a position that we call the locus, we see that it's possible that they have received at this locus, two alleles that are identical-by-descent. And here on the figure, it is shown for the case where they have received two alleles identical-by-descent from their grandfather Robert. So in fact, this alleles are identical-by-descent because Robert birthed the same allele to James and Albert, so his two sons. And then James and Albert passed this allele to Jack and Chloe. So this shared allele is a copy of a single allele that was present in Robert, but it could have also been from the grandmother Mary. And in fact, these two events are mutually exclusive. Jack and Chloe cannot share both an allele from Robert and Mary at a given locus. It is also possible that they shared no allele if James and Albert did not receive the same allele from Robert or Mary, or if they did not pass their shared allele to Jack and Chloe.