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Guido Barbujani

Publications and source records attributed to Guido Barbujani.

10 recordsLinked to original sources
PubMed2004

Estimating the impact of prehistoric admixture on the genome of Europeans.

We inferred past admixture processes in the European population from genetic diversity at eight loci, including autosomal, mitochondrial and Y-linked polymorphisms. Admixture coefficients were estimated from multilocus data, assuming that most current populations can be regarded as the result of a hybridization process among four or less potential parental populations. Two main components are apparent in the Europeans' genome, presumably corresponding to the contributions of the first, Paleolithic Europeans, and of the early, Neolithic farmers dispersing from the Near East. In addition, only a small fraction of the European alleles seems to come from North Africa, and a fourth component reflecting gene flow from Northern Asia is largely restricted to the northeast of the continent. The estimated Near Eastern contribution decreases as one moves from east to west, in agreement with the predictions of a model in which (Neolithic) immigrants from the Near East contributed a large share of the alleles in the genome of current Europeans. Several tests suggest that probable departures from the admixture models, due to factors such as choice of the putative parental populations and more complex demographic scenarios, may have affected our main estimates only to a limited extent.

Chromosomes, Human, Y↗
PubMed2004

The Etruscans: a population-genetic study.

The origins of the Etruscans, a non-Indo-European population of preclassical Italy, are unclear. There is broad agreement that their culture developed locally, but the Etruscans' evolutionary and migrational relationships are largely unknown. In this study, we determined mitochondrial DNA sequences in multiple clones derived from bone samples of 80 Etruscans who lived between the 7th and the 3rd centuries b.c. In the first phase of the study, we eliminated all specimens for which any of nine tests for validation of ancient DNA data raised the suspicion that either degradation or contamination by modern DNA might have occurred. On the basis of data from the remaining 30 individuals, the Etruscans appeared as genetically variable as modern populations. No significant heterogeneity emerged among archaeological sites or time periods, suggesting that different Etruscan communities shared not only a culture but also a mitochondrial gene pool. Genetic distances and sequence comparisons show closer evolutionary relationships with the eastern Mediterranean shores for the Etruscans than for modern Italian populations. All mitochondrial lineages observed among the Etruscans appear typically European or West Asian, but only a few haplotypes were found to have an exact match in a modern mitochondrial database, raising new questions about the Etruscans' fate after their assimilation into the Roman state.

Bone and Bones↗
PubMed2004

Molecular diversity at the CYP2D6 locus in the Mediterranean region.

Despite the importance of cytochrome P450 in the metabolism of many drugs, several aspects of molecular variation at one of the main loci coding for it, CYP2D6, have never been analysed so far. Here we show that it is possible to rapidly and efficiently genotype the main European allelic variants at this locus by a SNaPshot method identifying chromosomal rearrangements and nine single-nucleotide polymorphisms. Haplotypes could be reconstructed from data on 494 chromosomes in six populations of the Mediterranean region. High levels of linkage disequilibrium were found within the chromosome region screened, suggesting that CYP2D6 may be part of a genomic recombination block, and hence that, aside from unequal crossingover that led to large chromosomal rearrangements, its haplotype diversity essentially originated through the accumulation of mutations. With the only, albeit statistically insignificant, exception of Syria, haplotype frequencies do not differ among the populations studied, despite the presence among them of three well-known genetic outliers, which could be the result of common selective pressures playing a role in shaping CYP2D6 variation over the area of Europe that we surveyed.

Cytochrome P-450 CYP2D6↗
PubMed2004

Africans and Asians abroad: genetic diversity in Europe.

Besides its obvious intrinsic value, knowledge of population history, and of the demographic and evolutionary changes that accompany it, has proven fundamental to address applied research in human genetics. In this review we place current European genetic diversity in the context of the global human genome diversity and review the evidence supporting a recent African origin of the Europeans. We then discuss the results and the interpretation of genetic studies attempting to quantify the relative importance of various gene flow processes, both within Europe and from Asia into Europe, focusing especially on the initial, Paleolithic colonization of the continent, and on later, Paleolithic postglacial and Neolithic dispersals. Finally, we discuss how knowledge of the patterns of genetic diversity in Europe, and of their inferred generating processes, can be extremely useful in planning health care and in biomedical research.

Africa↗
PubMed2003

Evidence for a genetic discontinuity between Neandertals and 24,000-year-old anatomically modern Europeans.

During the late Pleistocene, early anatomically modern humans coexisted in Europe with the anatomically archaic Neandertals for some thousand years. Under the recent variants of the multiregional model of human evolution, modern and archaic forms were different but related populations within a single evolving species, and both have contributed to the gene pool of current humans. Conversely, the Out-of-Africa model considers the transition between Neandertals and anatomically modern humans as the result of a demographic replacement, and hence it predicts a genetic discontinuity between them. Following the most stringent current standards for validation of ancient DNA sequences, we typed the mtDNA hypervariable region I of two anatomically modern Homo sapiens sapiens individuals of the Cro-Magnon type dated at about 23 and 25 thousand years ago. Here we show that the mtDNAs of these individuals fall well within the range of variation of today's humans, but differ sharply from the available sequences of the chronologically closer Neandertals. This discontinuity is difficult to reconcile with the hypothesis that both Neandertals and early anatomically modern humans contributed to the current European gene pool.

Animals↗
PubMed2003

A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity.

Molecular genetic data contain information on the history of populations. Evidence of prehistoric demographic expansions has been detected in the mitochondrial diversity of most human populations and in a Y-chromosome STR analysis, but not in a previous study of 11 Y-chromosome SNPs in Europeans. In this paper, we show that mismatch distributions and tests of mutation/drift equilibrium based on up to 166 Y-chromosome SNPs, in 46 samples from all continents, also fail to support an increase of the male effective population size. Computer simulations show that the low nuclear versus mitochondrial mutation rates cannot explain these results. However, ascertainment bias, i.e., when only highly variable SNP sites are typed, may be concealing any Y SNPs evidence for a recent, but not an ancient, increase in male effective population sizes. The results of our SNP analyses can be reconciled with the expansion of male effective population sizes inferred from STR loci, and with mitochondrial evidence, by admitting that humans were essentially polygynous during much of their history. As a consequence, until recently only a few men may have contributed a large fraction of the Y-chromosome pool at every generation. The number of breeding males may have increased, and the variance of their reproductive success may have decreased, through a recent shift from polygyny to monogamy, which is supported by ethnological data and possibly accompanied the shift from mobile to sedentary communities.

Chromosomes, Human, Y↗
PubMed2002

Y genetic data support the Neolithic demic diffusion model.

There still is no general agreement on the origins of the European gene pool, even though Europe has been more thoroughly investigated than any other continent. In particular, there is continuing controversy about the relative contributions of European Palaeolithic hunter-gatherers and of migrant Near Eastern Neolithic farmers, who brought agriculture to Europe. Here, we apply a statistical framework that we have developed to obtain direct estimates of the contribution of these two groups at the time they met. We analyze a large dataset of 22 binary markers from the non-recombining region of the Y chromosome (NRY), by using a genealogical likelihood-based approach. The results reveal a significantly larger genetic contribution from Neolithic farmers than did previous indirect approaches based on the distribution of haplotypes selected by using post hoc criteria. We detect a significant decrease in admixture across the entire range between the Near East and Western Europe. We also argue that local hunter-gatherers contributed less than 30% in the original settlements. This finding leads us to reject a predominantly cultural transmission of agriculture. Instead, we argue that the demic diffusion model introduced by Ammerman and Cavalli-Sforza [Ammerman, A. J. & Cavalli-Sforza, L. L. (1984) The Neolithic Transition and the Genetics of Populations in Europe (Princeton Univ. Press, Princeton)] captures the major features of this dramatic episode in European prehistory.

Animals↗
PubMed2002

Patterns of human diversity, within and among continents, inferred from biallelic DNA polymorphisms.

Previous studies have reported that about 85% of human diversity at Short Tandem Repeat (STR) and Restriction Fragment Length Polymorphism (RFLP) autosomal loci is due to differences between individuals of the same population, whereas differences among continental groups account for only 10% of the overall genetic variance. These findings conflict with popular notions of distinct and relatively homogeneous human races, and may also call into question the apparent usefulness of ethnic classification in, for example, medical diagnostics. Here, we present new data on 21 Alu insertions in 32 populations. We analyze these data along with three other large, globally dispersed data sets consisting of apparently neutral biallelic nuclear markers, as well as with a beta-globin data set possibly subject to selection. We confirm the previous results for the autosomal data, and find a higher diversity among continents for Y-chromosome loci. We also extend the analyses to address two questions: (1) whether differences between continental groups, although small, are nevertheless large enough to confidently assign individuals to their continent on the basis of their genotypes; (2) whether the observed genotypes naturally cluster into continental or population groups when the sample source location is ignored. Using a range of statistical methods, we show that classification errors are at best around 30% for autosomal biallelic polymorphisms and 27% for the Y chromosome. Two data sets suggest the existence of three and four major groups of genotypes worldwide, respectively, and the two groupings are inconsistent. These results suggest that, at random biallelic loci, there is little evidence, if any, of a clear subdivision of humans into biologically defined groups.

Alleles↗
PubMed2002

Mitochondrial diversity in linguistic isolates of the Alps: a reappraisal.

In Stenico et al. (1996) we reported unusually high levels of mitochondrial diversity in the Alps. In particular, two communities of Ladin speakers appeared the most extreme European mitochondrial outliers at that time. Recently, it has been observed that some rare nucleotide substitutions occur repeatedly among those sequences, raising the possibility of systematic sequencing errors. No biological material was left from the previous study, and hence we had to sample new individuals from the same communities. Here, we present the HVSI sequence variation, along with haplogroup assignment based on restriction fragment length polymorphism (RFLP), in 20 Ladin speakers of Colle Santa Lucia. None of the new sequences displays substitutions at the sites viewed as problematic. However, Ladins still show high levels of mtDNA diversity, both within their community and with respect to other Europeans, and they can still be considered one of the main European mitochondrial outliers.

DNA, Mitochondrial↗