This is a very interesting paper about the global distribution of runs of homozygosity. Such runs are typical of recently inbred individuals (who have a greater chance of inheriting the same chunk of DNA from their related parents), but also occur because of population history (populations that today number in the millions are descended from a much smaller of ancestors, so even if one's parents aren't "relatives" in the genealogical sense, they, nonetheless contain chunks of identical DNA)."Old" inbreeding manifests itself in small chunks, as DNA chunks of ancestors get cut into ever finer pieces across the generations, while recently inbred individuals may have very long chunks.
Oceanians and Native Americans, for example, who are descended from relatively few founders because of the bottlenecks associated with crossing the Beringian/maritime voyages have an excess of short runs of homozygosity, but Native Americans also have long ones, suggestive of recent consanguinity.
Raw data can be found in the supplement.
PLoS ONE 5(11): e13996. doi:10.1371/journal.pone.0013996
Genomic Runs of Homozygosity Record Population History and Consanguinity
Mirna Kirin et al.
The human genome is characterised by many runs of homozygous genotypes, where identical haplotypes were inherited from each parent. The length of each run is determined partly by the number of generations since the common ancestor: offspring of cousin marriages have long runs of homozygosity (ROH), while the numerous shorter tracts relate to shared ancestry tens and hundreds of generations ago. Human populations have experienced a wide range of demographic histories and hold diverse cultural attitudes to consanguinity. In a global population dataset, genome-wide analysis of long and shorter ROH allows categorisation of the mainly indigenous populations sampled here into four major groups in which the majority of the population are inferred to have: (a) recent parental relatedness (south and west Asians); (b) shared parental ancestry arising hundreds to thousands of years ago through long term isolation and restricted effective population size (Ne), but little recent inbreeding (Oceanians); (c) both ancient and recent parental relatedness (Native Americans); and (d) only the background level of shared ancestry relating to continental Ne (predominantly urban Europeans and East Asians; lowest of all in sub-Saharan African agriculturalists), and the occasional cryptically inbred individual. Moreover, individuals can be positioned along axes representing this demographic historic space. Long runs of homozygosity are therefore a globally widespread and under-appreciated characteristic of our genomes, which record past consanguinity and population isolation and provide a distinctive record of the demographic history of an individual's ancestors. Individual ROH measures will also allow quantification of the disease risk arising from polygenic recessive effects.
Link
PLoS ONE 5(11): e13996. doi:10.1371/journal.pone.0013996
Genomic Runs of Homozygosity Record Population History and Consanguinity
Mirna Kirin et al.
The human genome is characterised by many runs of homozygous genotypes, where identical haplotypes were inherited from each parent. The length of each run is determined partly by the number of generations since the common ancestor: offspring of cousin marriages have long runs of homozygosity (ROH), while the numerous shorter tracts relate to shared ancestry tens and hundreds of generations ago. Human populations have experienced a wide range of demographic histories and hold diverse cultural attitudes to consanguinity. In a global population dataset, genome-wide analysis of long and shorter ROH allows categorisation of the mainly indigenous populations sampled here into four major groups in which the majority of the population are inferred to have: (a) recent parental relatedness (south and west Asians); (b) shared parental ancestry arising hundreds to thousands of years ago through long term isolation and restricted effective population size (Ne), but little recent inbreeding (Oceanians); (c) both ancient and recent parental relatedness (Native Americans); and (d) only the background level of shared ancestry relating to continental Ne (predominantly urban Europeans and East Asians; lowest of all in sub-Saharan African agriculturalists), and the occasional cryptically inbred individual. Moreover, individuals can be positioned along axes representing this demographic historic space. Long runs of homozygosity are therefore a globally widespread and under-appreciated characteristic of our genomes, which record past consanguinity and population isolation and provide a distinctive record of the demographic history of an individual's ancestors. Individual ROH measures will also allow quantification of the disease risk arising from polygenic recessive effects.
Link
