PMC:2668061 / 16924-23780 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/2668061","sourcedb":"PMC","sourceid":"2668061","source_url":"https://www.ncbi.nlm.nih.gov/pmc/2668061","text":"Results\nA total of 30 binary markers were typed in a set of 1140 Y chromosomes belonging to 18 populations from the Iberian Peninsula and the Balearic Islands (Figure 1). Of the 31 possible haplogroups defined by these markers, 20 were observed, but seven were represented by only one or two individuals. Thirteen haplogroups (each present at about 1% or greater overall) thus account for the vast majority of chromosomes, and one haplogroup, R1b3∗, is by far the most common (55%). When all chromosomes derived for the marker M269 are considered (R1b3∗ plus its sublineages R1b3b, R1b3d, and R1b3f), this figure approaches 66%.\nTo provide a context in which to consider the issue of a North African genetic contribution, we compiled haplogroup frequency data for four North African populations: Moroccans and Saharawi,34 plus Algerians and Tunisians47 (Figure 1). The most common haplogroup among North African populations is E3b2, representing 54% of the total of 361 chromosomes. To consider the contribution of Sephardic Jewish populations to the modern Iberian Peninsula, we compiled a set of 174 Y haplotypes from self-defined Sephardic males with ancestry in Mediterranean countries (see Subjects and Methods). This sample does not carry one predominant haplogroup but instead shows \u003e15% frequencies of three haplogroups: J2, J∗(xJ2), and G.\nHaplogroup frequencies in these Iberian, North African, and Sephardic Jewish populations are displayed graphically in Figure 2. The dramatic difference in haplogroup frequencies across the Gibraltar Strait34 is the most striking feature.\nA representation of these haplogroup-frequency data in the form of a multidimensional scaling (MDS) plot based on a pairwise FST matrix (Figure 3A) displays this distinction clearly, with the Iberian populations forming a clear cluster, the four North African populations clearly separated from them in the first dimension, and the Sephardic Jewish sample occupying an intermediate position. The Iberian populations most strongly differentiated from the non-Iberians are the Basques and the Gascons.\nAscertainment bias of the SNPs used to define haplogroups is a potential problem in Y-chromosomal diversity analysis (particularly because some Y-SNPs typed here were actually ascertained in Basques58,59) and can be addressed by consideration of pairwise RST estimates based on Y-STRs. Most of the Iberian samples had been previously typed with a set of 19 Y-STRs;46 this typing was extended to the full set of samples (Table S1). Inclusion of published data on the North African samples allowed a comparison over eight shared loci; data on the same eight loci were also available in the Sephardic Jewish sample. The MDS plot based on these data (Figure 3B) shows a similar pattern to that based on haplogroup frequencies, suggesting that ascertainment bias is not a major issue here.\nRemoval of the North African and Sephardic Jewish samples allows the distribution of Iberian populations to be seen more clearly (Figures 3C and 3D). Once more, the patterns based on haplogroup frequencies and Y-STR haplotypes (here based on 17 loci, with DYS385a and DYX385b removed) are broadly similar. In each case, the Basques are distinct from all other Iberian populations (and statistically significantly different, as judged by pairwise population-differentiation tests), with the exception of the Gascons, when haplogroup frequencies are considered.\nTo formally assess the impact of North African and Sephardic Jewish contributions on the indigenous population, we carried out admixture analysis, employing the mY estimator55 and treating the study populations as hybrids of three parental populations. We chose the Basques as the Iberian parental sample. This is justified on the basis of a relative absence of Muslim occupation of the Basque region17 and supported by the genetic distinctiveness of the Basque and neighboring Gascon samples (Figure 3). We chose the Moroccans as the North African parental sample, on the basis of historical evidence that entry to the Iberian Peninsula occurred via the Strait of Gibraltar17 and that the invading armies were largely native to Morocco. The third parental population was the Sephardic Jewish sample.\nMean ancestry proportions and their standard deviations for each population are represented schematically in Figure 4 (see Table S2 also). Considering the peninsula as a single population, the analysis unsurprisingly finds that the highest mean proportion of ancestry corresponds to the Basque parental population. However, this level is only 69.6%, leaving a remarkably high overall mean proportion of North African and Jewish ancestry forming the remainder. Mean North African admixture is 10.6%, with wide geographical variation (Figure 4, Table S2), ranging from zero in Gascony to 21.7% in Northwest Castile. Mean Sephardic Jewish admixture is 19.8%, varying from zero in Minorca to 36.3% in South Portugal (the value in Asturias is unlikely to be reliable, because of small sample size).\nTo examine admixture in more detail, we can compare Y-STR haplotypes within prominent lineages shared between the Iberian samples and the North African and Sephardic Jewish samples. A reduced-median network representing the eight-locus haplotypes within hgE3b2, the predominant haplogroup in North Africa, is shown in Figure 5a. The network is star-like, with a major core haplotype shared by 48 North Africans and 27 Iberians, plus the sole example of a Sephardic Jewish haplotype. In total, twelve of the 51 haplotypes are shared between North Africans and Iberians, but Iberians show a lower diversity (average squared difference [ASD] = 2.85) than North Africans (ASD = 9.13). This is consistent with a history of migration of North Africans to Iberia and introgression of hgE3b2 haplotypes, representing a subset of the North African diversity, into the indigenous population. A reciprocal example is provided by hgG (Figure 5B), frequent in the Sephardic Jewish sample. In this case, only two North African chromosomes belong to this haplogroup, but 7/48 haplotypes are shared between Sephardic Jewish and Iberian chromosomes, and the respective ASD values are similar, at 14.00 and 15.10. The high degree of haplotype sharing indicates introgression of Sephardic Jews into the indigenous Iberian population, but the similarity in haplotype diversity suggests that this was relatively ancient. Supporting a contribution of Sephardic Jewish patrilines to the Iberian population, shared STR haplotypes between the two within haplogroups E3b1, J∗, J2, and K∗ (data not shown, Table S1) were also observed. The mean proportion of identical haplotypes shared between the Sephardic Jewish sample and the Iberian samples is 3.6%, whereas the proportion for those shared between the Moroccan sample and the Iberian samples is 2.8%.","divisions":[{"label":"title","span":{"begin":0,"end":7}},{"label":"p","span":{"begin":8,"end":628}},{"label":"p","span":{"begin":629,"end":1348}},{"label":"p","span":{"begin":1349,"end":1586}},{"label":"p","span":{"begin":1587,"end":2086}},{"label":"p","span":{"begin":2087,"end":2871}},{"label":"p","span":{"begin":2872,"end":3431}},{"label":"p","span":{"begin":3432,"end":4232}},{"label":"p","span":{"begin":4233,"end":5026}}],"tracks":[{"project":"2_test","denotations":[{"id":"19061982-11254456-2048699","span":{"begin":819,"end":821},"obj":"11254456"},{"id":"19061982-15202071-2048700","span":{"begin":850,"end":852},"obj":"15202071"},{"id":"19061982-11254456-2048701","span":{"begin":1554,"end":1556},"obj":"11254456"},{"id":"19061982-9331370-2048702","span":{"begin":2288,"end":2290},"obj":"9331370"},{"id":"19061982-11062480-2048702","span":{"begin":2288,"end":2290},"obj":"11062480"},{"id":"19061982-11852201-2048703","span":{"begin":2451,"end":2453},"obj":"11852201"},{"id":"19061982-11264419-2048704","span":{"begin":3605,"end":3607},"obj":"11264419"}],"attributes":[{"subj":"19061982-11254456-2048699","pred":"source","obj":"2_test"},{"subj":"19061982-15202071-2048700","pred":"source","obj":"2_test"},{"subj":"19061982-11254456-2048701","pred":"source","obj":"2_test"},{"subj":"19061982-9331370-2048702","pred":"source","obj":"2_test"},{"subj":"19061982-11062480-2048702","pred":"source","obj":"2_test"},{"subj":"19061982-11852201-2048703","pred":"source","obj":"2_test"},{"subj":"19061982-11264419-2048704","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#a393ec","default":true}]}]}}