Not all homozygosity is created the same (way)

By Razib Khan | August 15, 2012 11:39 pm

Browsing the most recent issue of The American Journal of Human Genetics I stumbled upon a paper with some neat figures, Genomic Patterns of Homozygosity in Worldwide Human Populations. More specifically they focused on patterns of “runs of homozygosity” (ROH), that is, sequences of the genome which exhibited a strong bias toward homozygous SNPs. The figure above illustrates a pooled set of populations with individual variation in total length of ROH for aggregated from three classes, short, medium, and long ROHs. The small and medium length ROH exhibit the pattern of increasing total ROH as a function of distance from Africa. But not so with the large ROH. Why?

The figure below graphically illustrates what’s going on. Long ROH is found in Middle Eastern and South Asian populations with attested cultural patterns of inbreeding, as well as South American groups with very small effective population sizes. Short and medium runs are correlated with each other, because they are simply different quantitative manifestations of the same process in terms of generating ROH (e.g., bottlenecks, smaller effective population, etc.). In contrast, long ROH is due to the radical cranking down of effective population size which occurs during inbreeding.

CATEGORIZED UNDER: Genomics, Human Genomics
  • RedZenGenoist

    Am I the only one surprised and intrigued at the prevalence of long ROH among the South Americans? I’m drawn to recall a quote from Greg Cochran, about “Conan the Barbarian” author Robert E. Howard:

    “Given the chance (sufficient lack of information), American anthropologists assumed that the Mayans were peaceful astronomers. Howard would have assumed that they were just another blood-drenched snake cult: who came closer?”


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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