Genetic Chaos

Thursday, June 10, 2004

A pre-Columbian Y chromosome-specific transition and its implications for human evolutionary history

A polymorphic C-->T transition located on the human Y chromosome was found by the systematic comparative sequencing of Y-specific sequence-tagged sites by denaturing high-performance liquid chromatography. The results of genotyping representative global indigenous populations indicate that the locus is polymorphic exclusively within the Western Hemisphere. The pre-Columbian T allele occurs at > 90% frequency within the native South and Central American populations examined, while its occurrence in North America is approximately 50%. Concomitant genotyping at the polymorphic tetranucleotide microsatellite DYS19 locus revealed that the C-->T mutation displayed significant linkage disequilibrium with the 186-bp allele. The data suggest a single origin of linguistically diverse native Americans with subsequent haplotype differentiation within radiating indigenous populations as well as post-Columbian European and African gene flow. The mutation may have originated either in North America at a very early time during the expansion or before it, in the ancestral population(s) from which all Americans may have originated. The analysis of linkage of the DYS199 and the DYS19 tetranucleotide loci suggests that the C-->T mutation may have occurred around 30,000 years ago. We estimate the nucleotide diversity over 4.2 kb of the nonrecombining portion of the Y chromosome to be 0.00014. compared to autosomes, the majority of variation is due to the smaller effective population size of the Y chromosome rather than selective sweeps. There begins to emerge a pattern of pronounced geographical localization of Y-specific nucleotide substitution polymorphisms.

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mtDNA Analysis of a Prehistoric Oneota Population: Implications for the Peopling of the New World

mtDNA was successfully extracted from 108 individuals from the Norris Farms Oneota, a prehistoric Native American population, to compare the mtDNA diversity from a pre-Columbian population with contemporary Native American and Asian mtDNA lineages and to examine hypotheses about the peopling of the New World. Haplogroup and hypervariable region I sequence data indicate that the lineages from haplogroups A, B, C, and D are the most common among Native Americans but that they were not the only lineages brought into the New World from Asia. The mtDNA evidence does not support the three-wave hypothesis of migration into the New World but rather suggests a single "wave" of people with considerable mtDNA diversity that exhibits a signature of expansion 23,000-37,000 years ago.

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Mitochondrial DNA from Pre-Columbian Ciboneys From Cuba and the Prehistoric Colonization of the Caribbean

To assess the genetic affinities of extinct Ciboneys (also called Guanajuatabeys) from Cuba, 47 pre-Columbian skeletal samples belonging to this group were analyzed using ancient DNA techniques. At the time of European contact, the center and east of Cuba were occupied by agriculturalist Taino groups, while the west was mainly inhabited by Ciboneys, hunter-gatherers who have traditionally been considered a relic population descending from the initial colonization of the Caribbean. The mtDNA hypervariable region I (HVR-I) and haplogroup-specific markers were amplified and sequenced in 15 specimens using overlapping fragments; amplification from second extractions from the same sample, independent replication in different laboratories, and cloning of some PCR products support the authenticity of the sequences. Three of the five major mtDNA Amerindian lineages (A, C, and D) are present in the sample analyzed, in frequencies of 0.07, 0.60, and 0.33, respectively. Different phylogenetic analyses seem to suggest that the Caribbean most likely was populated from South America, although the data are still inconclusive, and Central American influences cannot be discarded. Our hypothesis is that the colonization of the Caribbean mainly took place in successive migration movements that emanated from the same area in South America, around the Lower Orinoco Valley: the first wave consisted of hunter-gatherer groups (ancestors of the Ciboneys), a subsequent wave of agriculturalists (ancestors of the Tainos), and a latter one of nomadic Carib warriors. However, further genetic studies are needed to confirm this scenario.

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The Use of Mitochondrial DNA to Discover Pre-Columbian Migrations to the Caribbean: Results for Puerto Rico and Expectations for the Dominican Republic

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Mitochrondial DNA in the Dominican Republic

A brief introduction by the editor: In the past, studies of the Taínos relied upon history, archaeology, and anthropology. Today, a new method of research is helping to shed light on ancient questions about them and their ancestors—genetics. The Human Genome Project, an international effort aimed at identifying and mapping the entire sequence of the more than 30,000 human genes and 3 billion chemical base pairs that make up human DNA, was completed ahead of its 2003 schedule. Today, scientists like Dr. Fernando Luna Calderón are using the new knowledge and methods learned from the Human Genome Project to trace human migrations, to identify human origins. Specifically, Luna Calderón proposes to clearly identify who the ancestors of the Taínos and other indigenous Caribbean peoples were, and their routes of migration and settlement. These are brand new studies, the results of which have not yet been realized. In this paper, Luna Calderón explains the biological base of the research and the methods he is using to obtain DNA samples and perform the required analyses on them.

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