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I was reading a couple of papers which talk about IBD (Identity by descent) among unrelated individuals (for eg. http://www.pnas.org/content/109/4/1193.long). However they do not seem to clearly define what they mean there. I was wondering how IBD is defined in such a context. I'd appreciate any help (especially suggested references to look this up).

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  • $\begingroup$ They are not close relatives of each other I suppose. You are right I think, there should be an exact definition. $\endgroup$ – inf3rno May 29 '15 at 21:15
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    $\begingroup$ I formulated an answer on this post that is very relevant. I was however quite confused and I am not sure whether or not several definitions of IBD exist in the literature. $\endgroup$ – Remi.b May 30 '15 at 2:28
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    $\begingroup$ In the context of GWA studies the IBD is usually different than what defined in population genetics. It represents the relatedness across individuals defined simply as the genotypic correlation between them. In other words, you run a linear regression using two individual genotypes to get an r-sq that can be interpreted as the proportion of similarity in their genetic material. r-squares of 0.5, 0.25 and 0.125 represent respectively parent–offspring, full-sibs, first cousins relationship. This is used as a control as GWAS statistical tools assume a population of unrelated individuals. $\endgroup$ – cagliari2005 May 30 '15 at 8:30

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