Casandrinos
09-20-2016, 06:37 PM
EDITED FOR GENETICS SUB-FORUM (Studies less than five years old allowed. No blog pieces. No Eupedia. The actual studies only).
- Professor Frank Grimes
This latter set of findings begs the question of whether this level of Sub-Saharan admixture is simply the carryover of Sub-Saharan African admixture embedded within a much larger recent North African contribution. It is this question that Botigué and colleagues successfully resolve (3). With the appropriate choice of sample sets, multiple independent analytic approaches converged on the conclusion that a relatively recent North African–specific, rather than Sub-Saharan, admixture has made a significant contribution to the population genomic structure of Europe, with a striking clinal pattern from prominence of such admixture in southwest Europe to vanishing in north and east Europe. With the reassuring exception of the Basque population isolate, the Iberian Peninsula showed the greatest imprint. Specifically, southwestern European populations averaged between 4% and 20% of their genomes assigned to a North African ancestral cluster, whereas this value did not exceed 2% in southeastern European populations
http://m.pnas.org/content/110/29/11668.full
North African Influences and Potential Bias in Case-Control Association Studies in the Spanish Population
Despite the limited genetic heterogeneity of Spanish populations, substantial evidences support that historical African influences have not affected them uniformly. Accounting for such population differences might be essential to reduce spurious results in association studies of genetic factors with disease. Using ancestry informative markers (AIMs), we aimed to measure the African influences in Spanish populations and to explore whether these might introduce statistical bias in population-based association studies.
Methodology/Principal Findings
We genotyped 93 AIMs in Spanish (from the Canary Islands and the Iberian Peninsula) and Northwest Africans, and conducted population and individual-based clustering analyses along with reference data from the HapMap, HGDP-CEPH, and other sources. We found significant differences for the Northwest African influence among Spanish populations from as low as ≈5% in Spanish from the Iberian Peninsula to as much as ≈17% in Canary Islanders, whereas the sub-Saharan African influence was negligible. Strikingly, the Northwest African ancestry showed a wide inter-individual variation in Canary Islanders ranging from 0% to 96%, reflecting the violent way the Islands were conquered and colonized by the Spanish in the XV century. As a consequence, a comparison of allele frequencies between Spanish samples from the Iberian Peninsula and the Canary Islands evidenced an excess of markers with significant differences. However, the inflation of p-values for the differences was adequately controlled by correcting for genetic ancestry estimates derived from a reduced number of AIMs.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0018389
- Professor Frank Grimes
This latter set of findings begs the question of whether this level of Sub-Saharan admixture is simply the carryover of Sub-Saharan African admixture embedded within a much larger recent North African contribution. It is this question that Botigué and colleagues successfully resolve (3). With the appropriate choice of sample sets, multiple independent analytic approaches converged on the conclusion that a relatively recent North African–specific, rather than Sub-Saharan, admixture has made a significant contribution to the population genomic structure of Europe, with a striking clinal pattern from prominence of such admixture in southwest Europe to vanishing in north and east Europe. With the reassuring exception of the Basque population isolate, the Iberian Peninsula showed the greatest imprint. Specifically, southwestern European populations averaged between 4% and 20% of their genomes assigned to a North African ancestral cluster, whereas this value did not exceed 2% in southeastern European populations
http://m.pnas.org/content/110/29/11668.full
North African Influences and Potential Bias in Case-Control Association Studies in the Spanish Population
Despite the limited genetic heterogeneity of Spanish populations, substantial evidences support that historical African influences have not affected them uniformly. Accounting for such population differences might be essential to reduce spurious results in association studies of genetic factors with disease. Using ancestry informative markers (AIMs), we aimed to measure the African influences in Spanish populations and to explore whether these might introduce statistical bias in population-based association studies.
Methodology/Principal Findings
We genotyped 93 AIMs in Spanish (from the Canary Islands and the Iberian Peninsula) and Northwest Africans, and conducted population and individual-based clustering analyses along with reference data from the HapMap, HGDP-CEPH, and other sources. We found significant differences for the Northwest African influence among Spanish populations from as low as ≈5% in Spanish from the Iberian Peninsula to as much as ≈17% in Canary Islanders, whereas the sub-Saharan African influence was negligible. Strikingly, the Northwest African ancestry showed a wide inter-individual variation in Canary Islanders ranging from 0% to 96%, reflecting the violent way the Islands were conquered and colonized by the Spanish in the XV century. As a consequence, a comparison of allele frequencies between Spanish samples from the Iberian Peninsula and the Canary Islands evidenced an excess of markers with significant differences. However, the inflation of p-values for the differences was adequately controlled by correcting for genetic ancestry estimates derived from a reduced number of AIMs.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0018389