1,721,283 research outputs found
A new estimator of population admixture based on molecular data
No full textWe propose here a new estimator of admixture coefficients based on the number of molecular differences between haplotypes, and thus suitable for molecular data like RFLPs or DNA sequences. We explor its potential and compare its performance against conventioanl estimators based on gene frequencies
Mitochondrial DNA sequence variation across linguistic and geographic boundaries in Italy
No full textA previous investigation demonstrated the existence of extensive allele frequency diversity within an area of northern Italy crossed by a linguistic (dialect) boundary and by the Po River, either of them or both presumably constraining gene flow. We obtained hair samples from 45 school pupils from 9 localities in that area and sequenced a 255-bp segment of the mtDNA D loop. Estimates of the minimum number of migration events from gene genealogies suggest that the linguistic barrier impaired gene flow more than the river did. However, an analysis of molecular variance (AMOVA) showed that most sequence diversity occurs within rather than between populations and that the differences between groups of populations, defined either by linguistic or geographic criteria, do not reach significance. Three areas of rapid genetic variation were identified; their locations suggest that populations of the western part of the study area evolved in relative isolation. Therefore mtDNA sequence variation does not seem to reflect the same processes--drift and presence of dispersal barriers--that led to the observed distributions of nuclear allele frequencies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
MATERNAL AND PATERNAL LINEAGES IN ALBANIA AND THE GENETIC STRUCTURE OF INDO-EUROPEAN POPULATIONS
No full textHuman genetic affinities for Y-chromosome P49a,f/TaqI haplotypes show strong correspondence with linguistics.
No full textNumerous population samples from around the world have been tested for Y chromosome–specific p49a,f/TaqI restriction polymorphisms. Here we review the literature as well as unpublished data on Y-chromosome p49a,f/ TaqI haplotypes and provide a new nomenclature unifying the notations used by different laboratories.We use this large data set to study worldwide genetic variability of human populations for this paternally transmitted chromosome segment. We observe, for the Y chromosome, an important level of population genetic structure among human populations (FST 5 .230, P ! .001), mainly due to genetic differences among distinct linguistic groups of populations (F 5 .246, P ! .001). CT A multivariate analysis based on genetic distances between populations shows that human population structure inferred from the Y chromosome corresponds broadly to language families (r 5 .567, P ! .001), in agreement with autosomal and mitochondrial data. Times of divergence of linguistic families, estimated from their internal level of genetic differentiation, are fairly concordant with current archaeological and linguistic hypotheses. Variability of the p49a,f/TaqI polymorphic marker is also significantly correlated with the geographic location of the populations (r 5 .613, P ! .001), reflecting the fact that distinct linguistic groups generally also occupy distinct geographic areas. Comparison of Y-chromosome and mtDNA RFLPs in a restricted set of populations shows a globally high level of congruence, but it also allows identification of unequal maternal and paternal contributions to the gene pool of several populations
Evolutionary correlation between control region sequence and restriction polymorphisms in the mitochondrial genome of a large Senegalese Mandenka sample
No full textWe present here the first comparative analysis at the population level between Restriction Fragment Length Polymorphism (RFLP) and control region sequence polymorphism in a large and homogeneous Senegalese Mandenka sample. Eleven RFLP haplotypes and 60 different sequences are found in 119 individuals, revealing that a very high level of mtDNA diversity can be maintained in a small population. A sequence neighbor-joining tree and an analysis of molecular variance show that sequences associated with a given restriction haplotype are evolutionarily highly correlated: sequencing generally leads to the subtyping of RFLP haplotypes. Evolutionary relationships among RFLP haplotypes inferred from restriction site differences are in good agreement with those inferred from sequence data. A single difference is observed and is likely due to a single restriction homoplasy having occurred in the control region. Selective neutrality tests on both RFLP and sequence data accept the hypotheses of mtDNA neutrality and population equilibrium. The deep coalescence times (exceeding 50,000 yr) of sequences associated with the two most frequent restriction haplotypes confirm that the Niokolo Mandenka population has not passed through a recent bottleneck and that gene flow is maintained among West African populations despite ethnic differences
Different genetic components in the Ethiopian population, identified by mtDNA and Y-chromosome polymorphisms.
No full textSeventy-seven Ethiopians were investigated for mtDNA and Y chromosome–specific variations, in order to (1) define the different maternal and paternal components of the Ethiopian gene pool, (2) infer the origins of these maternal and paternal lineages and estimate their relative contributions, and (3) obtain information about ancient populations living in Ethiopia. The mtDNA was studied for the RFLPs relative to the six classical enzymes (HpaI, BamHI, HaeII, MspI, AvaII, and HincII) that identify the African haplogroup L and the Caucasoid haplogroups I and T. The sample was also examined at restriction sites that define the other Caucasoid haplogroups (H, U, V, W, X, J, and K) and for the simultaneous presence of the DdeI10394 and AluI10397 sites, which defines the Asian haplogroup M. Four polymorphic systems were examined on the Y chromosome: the TaqI/12f2 and the 49a,f RFLPs, the Y Alu polymorphic element (DYS287), and the sY81-A/G (DYS271) polymorphism. For comparison, the last two Y polymorphisms were also examined in 87 Senegalese previously classified for the two TaqI RFLPs. Results from these markers led to the hypothesis that the Ethiopian population (1) experienced Caucasoid gene flow mainly through males, (2) contains African components ascribable to Bantu migrations and to an in situ differentiation process from an ancestral African gene pool, and (3) exhibits some Y-chromosome affinities with the Tsumkwe San (a very ancient African group). Our finding of a high (20%) frequency of the “Asian” DdeI10394AluI10397 (11) mtDNA haplotype in Ethiopia is discussed in terms of the “out of Africa” model
European phylogeography of the epiphytic lichen fungus Lobaria pulmonaria and its green algal symbiont
No full textIn lichen symbiosis, fungal and algal partners form close associations, often codispersed by vegetative propagules. Due to the particular interdependence, processes such as colonization, dispersal or genetic drift are expected to result in congruent patterns of genetic structure in the symbionts. To study the population structure of an obligate symbiotic system in Europe, we genotyped the fungal and algal symbionts of the epiphytic lichen Lobaria pulmonaria at eight and seven microsatellite loci, respectively, and analysed about 4300 L. pulmonaria thalli from 142 populations from the species' European distribution range. Based on a centroid approach, which localizes centres of genetic differentiation with a high frequency of geographically restricted alleles, we identified the South Italy-Balkan region as the primary glacial refugial area of the lichen symbiosis. Procrustean rotation analysis and a distance congruence test between the fungal and algal population graphs indicated general concordance between the phylogeographies of the symbionts. The incongruent patterns found in areas of postglacial recolonization may show the presence of an additional refugial area for the fungal symbiont, and the impact that horizontal photobiont transmission and different mutation rates of the symbionts have on their genotypic associations at a continental scale. © 2012 Blackwell Publishing Ltd
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