1,721,048 research outputs found
Geographic homogeneity and non-equilibrium patterns of mtDNA sequences in Tuscany, Italy
No full textThe geographical distribution of 49 mtDNA sequences from 22 localities in Southern Tuscany, Italy, was studied by molecular analysis of variance, by a new spatial autocorrelation statistic specifically designed for sequence data and by reconstructing genealogies of haplotypes. All these methods indicated a high homogeneity of populations. Nevertheless, genetic variability showed significant departure from equilibrium expectations, in agreement with the predicted effects of a population expansion. We suggest that a past population expansion that was probably associated with a migrational wave and with local gene flow between localities prevented spatial structuring in Southern Tuscany
Genetic history of cystic fibrosis mutations in Italy.Regional distribution.
No full textEarlier analysis of the Italian population showed patterns of genetic differentiation that were interpreted as being the result of population settlements going back to pre-Roman times. DNA disease mutations may be a powerful tool in further testing this hypothesis since the analysis of diseased individuals can detect variants too rare to be resolved in normal individuals. We present data on the relative frequencies of 60 cystic fibrosis (CF) mutations in Italy and the geographical distribution of the 12 most frequent CF mutations screened in 3492 CF chromosomes originating in 13 Italian regions. The 12 most frequent mutations characterize about 73% of the Italian CF chromosomes. The most common mutation, ΔF508, has an average frequency of 51%, followed by N1303K and G542X, both with average frequencies around 5%. Multivariate analyses show that the relative frequencies of CF mutations are heterogeneous among Italian regions, and that this heterogeneity is weakly correlated with the geographical pattern of non-DNA 'classical' genetic markers. The northern regions are well differentiated from the central-southern regions and within the former group the western and eastern regions are remarkably distinct. Moreover, Sardinia shows the presence of mutation T338I, which seems absent in any other European CF chromosome. The north-western regions of Italy, characterized by the mutation 1717-1G→A, were under Celtic influence, while the north-east regions, characterized by the mutations R1162X, 2183AA→G and 711 + 5G→X, were under the influence of the Venetic culture
Reconstruction of prehistory on the basis of genetic data
No full textIn their letter, Torroni et al. (2000) express a radical
disagreement with the assumptions, methods, and conclusions
of Simoni et al.’s (2000) article. We think that
their many criticisms can be reduced to four points:
1. Haplogroups have been incorrectly defined, and
therefore the spatial autocorrelation analysis (SAAP) of
their frequencies is flawed;
2. Aside from these errors, the frequencies of haplogroup
J and of superhaplogroup JT do not match previous
reports;
3. Only 22 polymorphic sites have been considered,
and therefore the results of AIDA are flawed;
4. Meaningful patterns of mtDNA diversity can only
be identified by the analysis of the distributions of recent
mutations
Do Basque- and Caucasian-speaking populations share non-Indo-European ancestors?
No full textGenetic evidence is consistent with the view that the Indo-European languages were propagated in Europe by the diffusion of early farmers. The existence of phylogenetic relationships between European populations speaking other languages has been proposed on linguistic and archaeological grounds, and is here tested by analyzing allele frequencies at ten polymorphic protein and blood group loci. Genetic distances between speakers of Basque and Caucasian languages are compared with those between controls, i.e. contiguous populations speaking Indo-European and Altaic. Although some statistical tests show an excess of genetic similarity between Basque and South Caucasian speakers, most results do not support their common origin. If the Basques and the Caucasian-speaking populations share common ancestors, recent evolutionary phenomena must have caused divergence between them, so that their gene frequencies do not appear more similar now than those of random pairs of populations separated by the same geographic distance
The Mediterranean paradox for susceptibility factors in coronary heart disease extends to genetics
No full textThe incidence of coronary heart disease (CHD) shows a North to South gradient in Europe. We tested whether that
gradient could be accounted for by the distribution of putative susceptibility genotypes. We correlated the published
frequencies of susceptibility genotypes for the genes most often associated with CHD (ACE, AGT, APOE, F2, F5,
MTHFR, PON1, and SERPINE1) with the incidence of the disease, controlling for the effects of smoking, systolic
pressure, total cholesterol, and body-mass index. In three polymorphisms a negative correlation between the incidence
of CHD and the frequency of a suceptibility genotype was observed. For ACE this correlation was significantly negative
even when discounting classical susceptibility factors. This suggests that some alleles described as susceptibility factors
cannot account for disease incidence at the population level. A genetic component must be added to the “Mediterranean
paradox”: genetic variants deemed to be risk factors for CHD show a geographical pattern uncorrelated with the disease
incidence. This pattern can be understood from the history of populations which has shaped the genetic diversity of the
European populations in North-South clines, similar to what is observed for CHD incidence, which will tend to create
spurious correlations with polymorphisms related, or not related, to the disease
Sequence diversity of the control region of mitochondrial DNA in tuscany and its implications for the peopling of Europe
No full textThe control region of mitochondrial DNA has been widely studied in various human populations. This paper reports sequence data for hypervariable segments 1 and 2 of the control region from a population from southern Tuscany (Italy). The results confirm the high variability of the control region, with 43 different haplotypes in 49 individuals sampled. The comparison of this set of data with other European populations allows the reconstruction of the population history of Tuscany. Independent approaches, such as the estimation of haplotype diversity, mean pairwise differences, genetic distances and discriminant analysis, place the Tuscan sample in an intermediate position between sequences from culturally or geographically isolated regions of Europe (Sardinia, the Basque Country, Britain) and those from the Middle East. In spite of the remarkable genetic homogeneity in Europe, a degree of variability is shown by local European populations and homogeneity increases with the relative isolation of the population. The pattern of mitochondrial variation in Tuscany indicates the persistence of an ancient European component subsequently enriched by migrational waves, possibly from the Middle East. (C) 1998 Wiley-Liss, Inc
Geographic patterns of mtDNA diversity in Europe
No full textGenetic diversity in Europe has been interpreted as a
reflection of phenomena occurring during the Paleolithic
(»45,000 years before the present [BP]), Mesolithic
(»18,000 years BP), and Neolithic (»10,000 years BP)
periods. A crucial role of the Neolithic demographic
transition is supported by the analysis of most nuclear
loci, but the interpretation of mtDNA evidence is controversial.
More than 2,600 sequences of the first hypervariable
mitochondrial control region were analyzed
for geographic patterns in samples from Europe, the
Near East, and the Caucasus. Two autocorrelation statistics
were used, one based on allele-frequency differences
between samples and the other based on both sequence
and frequency differences between alleles. In the
global analysis, limited geographic patterning was observed,
which could largely be attributed to a marked
difference between the Saami and all other populations.
The distribution of the zones of highest mitochondrial
variation (genetic boundaries) confirmed that the Saami
are sharply differentiated from an otherwise rather homogeneous
set of European samples. However, an area
of significant clinal variation was identified around the
Mediterranean Sea (and not in the north), even though
the differences between northern and southern populations
were insignificant. Both a Paleolithic expansion
and the Neolithic demic diffusion of farmers could have
determined a longitudinal cline of mtDNA diversity.
However, additional phenomena must be considered in
both models, to account both for the north-south differences
and for the greater geographic scope of clinal
patterns at nuclear loci. Conversely, two predicted consequences
of models of Mesolithic reexpansion from glacial
refugia were not observed in the present study
On the origins and admixture of Malagasy: new evidence from high-resolution analyses of paternal and maternal lineages
No full textThe Malagasy have been shown to be a genetically admixed population combining parental lineages with African and South East Asian ancestry. In the present paper, we fit the Malagasy admixture history in a highly resolved phylogeographic framework by typing a large set of mitochondrial DNA and Y DNA markers in unrelated individuals from inland (Merina) and coastal (Antandroy, Antanosy, and Antaisaka) ethnic groups. This allowed performance of a multilevel analysis in which the diversity among main ethnic divisions, lineage ancestries, and modes of inheritance could be concurrently evaluated. Admixture was confirmed to result from the encounter of African and Southeast Asian people with minor recent male contributions from Europe. However, new scenarios are depicted about Malagasy admixture history. The distribution of ancestral components was ethnic and sex biased, with the Asian ancestry appearing more conserved in the female than in the male gene pool and in inland than in coastal groups. A statistic based on haplotype sharing (D(HS)), showing low sampling error and time linearity over the last 200 generations, was introduced here for the first time and helped to integrate our results with linguistic and archeological data. The focus about the origin of Malagasy lineages was enlarged in space and pushed back in time. Homelands could not be pinpointed but appeared to comprise two vast areas containing different populations from sub-Saharan Africa and South East Asia. The pattern of diffusion of uniparental lineages was compatible with at least two events: a primary admixture of proto-Malay people with Bantu speakers bearing a western-like pool of haplotypes, followed by a secondary flow of Southeastern Bantu speakers unpaired for gender (mainly male driven) and geography (mainly coastal)
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
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