Multiple origins of Tibetan Y chromosomes

Genetic polymorphisms of the drug-metabolizing enzyme CYP2J2 in a Tibetan population

As an important metabolic enzyme, it is necessary to investigate the genetic polymorphisms of CYP2J2 among healthy Tibetan individuals. Genetic polymorphisms of CYP2J2 could affect enzyme activity and lead to differences among individual responses to drugs.We sequenced the whole gene of CYP2J2 in 100 unrelated, healthy Tibetan volunteers from the Tibet Autonomous Region and screened for genetic variants in the promoters, introns, exons, and the 3'-UTR regions.We detected 4 novel genetic polymorphisms of the CYP2J2 gene. The allelic frequencies of CYP2D6*1 and *7 were 0.955 and 0.045, respectively. CYP2D6*1/*7 decreased the activity of CYP2J2 and was expressed in 9% of the sample population.Our results provided basic data about CYP2J2 polymorphisms in a Tibetan population, suggested that the enzymatic activities of CYP2J2 might be different within the ethnic group, and offered a theoretical basis for individualized medical treatment and drug genomics studies.

Investigating the genetic diversity and affinities of historical populations of Tibet

This study elucidates Y chromosome distribution patterns in the three general provincial populations of historical Tibet, Amdo (n = 88), Dotoe (n = 109) and U-Tsang (n = 153) against the backdrop of 37 Asian reference populations. The central aim of this study is to investigate the genetic affinities of the three historical Tibetan populations among themselves and to neighboring populations. Y-SNP and Y-STR profiles were assessed in these historical populations. Correspondence analyses (CA) were generated with Y-SNP haplogroup data. Y-STR haplotypes were determined and employed to generate multidimensional scaling (MDS) plots based on Rst distances. Frequency contour maps of informative Y haplogroups were constructed to visualize the distributions of specific chromosome types. Network analyses based on Y-STR profiles of individuals under specific Y haplogroups were generated to examine the genetic heterogeneity among populations. Average gene diversity values and other parameters of population genetics interest were estimated to characterize the populations. The Y chromosomal results generated in this study indicate that using two sets of markers (Y-SNP, and Y-STR) the three Tibetan populations are genetically distinct. In addition, U-Tsang displays the highest gene diversity, followed by Amdo and Dotoe. The results of this transcontinental biogeographical investigation also indicate various degrees of paternal genetic affinities among these three Tibetan populations depending on the type of loci (Y-SNP or Y-STR) analyzed. The CA generated with Y-SNP haplogroup data demonstrates that Amdo and U-Tsang are closer to each other than to any neighboring non-Tibetan group. In contrast, the MDS plot based on Y-STR haplotypes displays Rst distances that are much shorter between U-Tsang and its geographic nearby populations of Ladakh, Punjab, Kathmandu and Newar than between it and Amdo. Moreover, although Dotoe is isolated from all other groups using both types of marker systems, it lies nearer to the other Tibetan collections in the Y-SNP CA than in the Y-STR MDS plot. High resolution and shallow evolutionary time frames engendered by Y-STR based analyses may reflect a more recent demographic history than that delineated by the more conserved Y-SNP markers.

Evolutionary significance of selected EDAR variants in Tibetan high-altitude adaptations

Humans have been exposed to many environmental challenges since their evolutionary origins in Africa and subsequent migrations to the rest of the world. A severe environmental challenge to human migrants was hypoxia caused by low barometric oxygen pressure at high altitudes. Several genome-wide scans have elucidated the genetic basis of human high-altitude adaptations. However, the dearth of functional variant information has led to the successful association of only a few candidate genes. In the present study, we employed a candidate gene approach and re-sequenced the EDAR locus in 45 Tibetan individuals to identify mutations involved in hypoxia adaptation. We identified 10 and five quantitative trait-associated mutations for oxygen saturation (SaO₂) and blood platelet count, respectively, at the EDAR locus. Among these, rs10865026 and rs3749110 (associated with SaO₂ and platelet count, respectively) were identified as functional candidate targets. These data demonstrate that EDAR has undergone natural selection in recent human history and indicate an important role of EDAR variants in Tibetan high-altitude adaptations.

Genetic structure of Qiangic populations residing in the western Sichuan corridor

The Qiangic languages in western Sichuan (WSC) are believed to be the oldest branch of the Sino-Tibetan linguistic family, and therefore, all Sino-Tibetan populations might have originated in WSC. However, very few genetic investigations have been done on Qiangic populations and no genetic evidences for the origin of Sino-Tibetan populations have been provided. By using the informative Y chromosome and mitochondrial DNA (mtDNA) markers, we analyzed the genetic structure of Qiangic populations. Our results revealed a predominantly Northern Asian-specific component in Qiangic populations, especially in maternal lineages. The Qiangic populations are an admixture of the northward migrations of East Asian initial settlers with Y chromosome haplogroup D (D1-M15 and the later originated D3a-P47) in the late Paleolithic age, and the southward Di-Qiang people with dominant haplogroup O3a2c1*-M134 and O3a2c1a-M117 in the Neolithic Age.

Differences in mtDNA whole sequence between Tibetan and Han populations suggesting adaptive selection to high altitude

We performed a mitochondrial whole-genome comparison study in 40 Tibetan and 50 Han Chinese. All subjects could be classified into 13 haplogroups pertained to the Macrohaplogroup M and N that pitched different quadrants by principal component analysis. We observed a difference in the M9 haplogroup and identified 18 significant variants by comparing whole sequences between Tibetan and Han populations. Variants in ND2, COX2, tRNA alanine and 12S rRNA were predicted to confer increased protein stability in Tibetans. We compared the base substitutions of nonsynonymous (NS) versus synonymous (S) of 13 protein-encoding genes and found the NS/S values of the ATP6, ATP8, and Cyt b genes were larger (>1) in Tibetans than that in Han population. Our findings provide clues for the existence of adaptive selection for the ATP6, ATP8, Cyt b, ND2, COX2, tRNA alanine and 12S rRNA genes in Tibetans which likely contributed to adaptation to their specific geographic environment, such as high altitude.

The local origin of the Tibetan pig and additional insights into the origin of Asian pigs

BACKGROUND

The domestic pig currently indigenous to the Tibetan highlands is supposed to have been introduced during a continuous period of colonization by the ancestors of modern Tibetans. However, there is no direct genetic evidence of either the local origin or exotic migration of the Tibetan pig.

METHODS AND FINDINGS

We analyzed mtDNA hypervariable segment I (HVI) variation of 218 individuals from seven Tibetan pig populations and 1,737 reported mtDNA sequences from domestic pigs and wild boars across Asia. The Bayesian consensus tree revealed a main haplogroup M and twelve minor haplogroups, which suggested a large number of small scale in situ domestication episodes. In particular, haplogroups D1 and D6 represented two highly divergent lineages in the Tibetan highlands and Island Southeastern Asia, respectively. Network analysis of haplogroup M further revealed one main subhaplogroup M1 and two minor subhaplogroups M2 and M3. Intriguingly, M2 was mainly distributed in Southeastern Asia, suggesting for a local origin. Similar with haplogroup D6, M3 was mainly restricted in Island Southeastern Asia. This pattern suggested that Island Southeastern Asia, but not Southeastern Asia, might be the center of domestication of the so-called Pacific clade (M3 and D6 here) described in previous studies. Diversity gradient analysis of major subhaplogroup M1 suggested three local origins in Southeastern Asia, the middle and downstream regions of the Yangtze River, and the Tibetan highlands, respectively.

CONCLUSIONS

We identified two new origin centers for domestic pigs in the Tibetan highlands and in the Island Southeastern Asian region.

Y-chromosome O3 haplogroup diversity in Sino-Tibetan populations reveals two migration routes into the eastern Himalayas

The eastern Himalayas are located near the southern entrance through which early modern humans expanded into East Asia. The genetic structure in this region is therefore of great importance in the study of East Asian origins. However, few genetic studies have been performed on the Sino-Tibetan populations (Luoba and Deng) in this region. Here, we analyzed the Y-chromosome diversity of the two populations. The Luoba possessed haplogroups D, N, O, J, Q, and R, indicating gene flow from Tibetans, as well as the western and northern Eurasians. The Deng exhibited haplogroups O, D, N, and C, similar to most Sino-Tibetan populations in the east. Short tandem repeat (STR) diversity within the dominant haplogroup O3 in Sino-Tibetan populations showed that the Luoba are genetically close to Tibetans and the Deng are close to the Qiang. The Qiang had the greatest diversity of Sino-Tibetan populations, supporting the view of this population being the oldest in the family. The lowest diversity occurred in the eastern Himalayas, suggesting that this area was an endpoint for the expansion of Sino-Tibetan people. Thus, we have shown that populations with haplogroup O3 moved into the eastern Himalayas through at least two routes.

Y-chromosomal microsatellite diversity in three culturally defined regions of historical Tibet

In the present study, we analyzed 17 Y-STR loci in 350 Tibetan males from three culturally defined regions of historical Tibet: Amdo (88), Kham (109) and U-Tsang (153). A total of 299 haplotypes were observed, 272 (90.9%) of which were unique. Only one Y-STR profile is shared across the three Tibetan groups and, incidentally, is also the most frequent haplotype (4.0%), represented by two, five and seven individuals from U-Tsang, Kham and Amdo, respectively. The overall haplotype diversity for the three Tibetan populations at 17 Y-STR loci was 0.9978 and the corresponding values for the extended (11-loci) and minimal (9-loci) haplotypes were 0.9935 and 0.9909, respectively. Both neighbor-joining and Rst pairwise analyses suggest a close genetic relationship between the Amdo and Kham populations, while U-Tsang is genetically distinct from the aforementioned groups. The results demonstrate that the 17 Y-STR loci analyzed are highly polymorphic in all three Tibetan populations examined and hence useful for forensic cases, paternity testing and population genetic studies.

Y-chromosome haplogroup diversity in the sub-Himalayan Terai and Duars populations of East India

The sub-Himalayan Terai and Duars, the important outermost zones comprising the plains of East India, are known as the reservoirs of ethnic diversity. Analysis of the paternal genetic diversity of the populations inhabiting these regions and their genetic relationships with adjacent Himalayan and other Asian populations has not been addressed empirically. In the present investigation, we undertook a Y-chromosome phylogeographic study on 10 populations (n=375) representing four different linguistic groups from the sub-Himalayan Terai and Duars regions of East India. The high-resolution analysis of Y-chromosome haplogroup variations based on 76 binary markers revealed that the sub-Himalayan paternal gene pool is extremely heterogeneous. Three major haplogroups, namely H, O and R, are shared across the four linguistic groups. The Indo-European-speaking castes exhibit more haplogroup diversity than the tribal groups. The findings of the present investigation suggest that the sub-Himalayan gene pools have received predominant Southeast Asian contribution. In addition, the presence of Northeast and South Asian signatures illustrate multiple events of population migrations as well as extensive genetic admixture amongst the linguistic groups.

Y-STR diversity in the Himalayas

Linguistic and ethnic diversity throughout the Himalayas suggests that this mountain range played an important role in shaping the genetic landscapes of the region. Previous Y-chromosome work revealed that the Himalayas acted as a biased bidirectional barrier to gene flow across the cordillera. In the present study, 17 Y-chromosomal short tandem repeat (Y-STR) loci included in the AmpFlSTR® Yfiler kit were analyzed in 344 unrelated males from three Nepalese populations (Tamang, Newar, and Kathmandu) and a general collection from Tibet. The latter displays the highest haplotype diversity (0.9990) followed by Kathmandu (0.9977), Newar (0.9570), and Tamang (0.9545). The overall haplotype diversity for the Himalayan populations at 17 Y-STR loci was 0.9973, and the corresponding values for the extended (11 loci) and minimal (nine loci) haplotypes were 0.9955 and 0.9942, respectively. No Y-STR profiles are shared across the four Himalayan collections at the 17-, 11-, and nine-locus resolutions considered, indicating a lack of recent gene flow among them. Phylogenetic analyses support our previous findings that Kathmandu, and to some extent Newar, received significant genetic influence from India while Tamang and Tibet exhibit limited or no gene flow from the subcontinent. A median-joining network of haplogroup O3a3c-M134 based on 15 Y-STR loci from our four Himalayan populations suggests either a male founder effect in Tamang, possibly from Tibet, or a recent bottleneck following their arrival south of the Himalayas from Tibet leading to their highly reduced Y single-nucleotide polymorphism and Y-STR diversity. The genetic uniqueness of the four Himalayan populations examined in this study merits the creation of separate databases for individual identification, parentage analysis, and population genetic studies.

Natural selection on EPAS1 (HIF2alpha) associated with low hemoglobin concentration in Tibetan highlanders

By impairing both function and survival, the severe reduction in oxygen availability associated with high-altitude environments is likely to act as an agent of natural selection. We used genomic and candidate gene approaches to search for evidence of such genetic selection. First, a genome-wide allelic differentiation scan (GWADS) comparing indigenous highlanders of the Tibetan Plateau (3,200-3,500 m) with closely related lowland Han revealed a genome-wide significant divergence across eight SNPs located near EPAS1. This gene encodes the transcription factor HIF2alpha, which stimulates production of red blood cells and thus increases the concentration of hemoglobin in blood. Second, in a separate cohort of Tibetans residing at 4,200 m, we identified 31 EPAS1 SNPs in high linkage disequilibrium that correlated significantly with hemoglobin concentration. The sex-adjusted hemoglobin concentration was, on average, 0.8 g/dL lower in the major allele homozygotes compared with the heterozygotes. These findings were replicated in a third cohort of Tibetans residing at 4,300 m. The alleles associating with lower hemoglobin concentrations were correlated with the signal from the GWADS study and were observed at greatly elevated frequencies in the Tibetan cohorts compared with the Han. High hemoglobin concentrations are a cardinal feature of chronic mountain sickness offering one plausible mechanism for selection. Alternatively, as EPAS1 is pleiotropic in its effects, selection may have operated on some other aspect of the phenotype. Whichever of these explanations is correct, the evidence for genetic selection at the EPAS1 locus from the GWADS study is supported by the replicated studies associating function with the allelic variants.

Mitochondrial genome evidence reveals successful Late Paleolithic settlement on the Tibetan Plateau

Due to its numerous environmental extremes, the Tibetan Plateau--the world's highest plateau--is one of the most challenging areas of modern human settlement. Archaeological evidence dates the earliest settlement on the plateau to the Late Paleolithic, while previous genetic studies have traced the colonization event(s) to no earlier than the Neolithic. To explore whether the genetic continuity on the plateau has an exclusively Neolithic time depth, we studied mitochondrial DNA (mtDNA) genome variation within 6 regional Tibetan populations sampled from Tibet and neighboring areas. Our results confirm that the vast majority of Tibetan matrilineal components can trace their ancestry to Epipaleolithic and Neolithic immigrants from northern China during the mid-Holocene. Significantly, we also identified an infrequent novel haplogroup, M16, that branched off directly from the Eurasian M founder type. Its nearly exclusive distribution in Tibetan populations and ancient age (>21 kya) suggest that M16 may represent the genetic relics of the Late Paleolithic inhabitants on the plateau. This partial genetic continuity between the Paleolithic inhabitants and the contemporary Tibetan populations bridges the results and inferences from archaeology, history, and genetics.

Genetic insights into the origins of Tibeto-Burman populations in the Himalayas

The Himalayan mountain range has played a dual role in shaping the genetic landscape of the region by (1) delineating east-west migrations including the Silk Road and (2) restricting human dispersals, especially from the Indian subcontinent into the Tibetan plateau. In this study, 15 hypervariable autosomal STR loci were employed to evaluate the genetic relationships of three populations from Nepal (Kathmandu, Newar and Tamang) and a general collection from Tibet. These Himalayan groups were compared to geographically targeted worldwide populations as well as Tibeto-Burman (TB) speaking groups from Northeast India. Our results suggest a Northeast Asian origin for the Himalayan populations with subsequent gene flow from South Asia into the Kathmandu valley and the Newar population, corroborating a previous Y-chromosome study. In contrast, Tamang and Tibet exhibit limited genetic contributions from South Asia, possibly due to the orographic obstacle presented by the Himalayan massif. The TB groups from Northeast India are genetically distinct compared to their counterparts from the Himalayas probably resulting from prolonged isolation and/or founder effects.

Y chromosome evidence of earliest modern human settlement in East Asia and multiple origins of Tibetan and Japanese populations

Background

The phylogeography of the Y chromosome in Asia previously suggested that modern humans of African origin initially settled in mainland southern East Asia, and about 25,000–30,000 years ago, migrated northward, spreading throughout East Asia. However, the fragmented distribution of one East Asian specific Y chromosome lineage (D-M174), which is found at high frequencies only in Tibet, Japan and the Andaman Islands, is inconsistent with this scenario.

Results

In this study, we collected more than 5,000 male samples from 73 East Asian populations and reconstructed the phylogeography of the D-M174 lineage. Our results suggest that D-M174 represents an extremely ancient lineage of modern humans in East Asia, and a deep divergence was observed between northern and southern populations.

Conclusion

We proposed that D-M174 has a southern origin and its northward expansion occurred about 60,000 years ago, predating the northward migration of other major East Asian lineages. The Neolithic expansion of Han culture and the last glacial maximum are likely the key factors leading to the current relic distribution of D-M174 in East Asia. The Tibetan and Japanese populations are the admixture of two ancient populations represented by two major East Asian specific Y chromosome lineages, the O and D haplogroups.

Genetic studies of human diversity in East Asia

East Asia is one of the most important regions for studying evolution and genetic diversity of human populations. Recognizing the relevance of characterizing the genetic diversity and structure of East Asian populations for understanding their genetic history and designing and interpreting genetic studies of human diseases, in recent years researchers in China have made substantial efforts to collect samples and generate data especially for markers on Y chromosomes and mtDNA. The hallmark of these efforts is the discovery and confirmation of consistent distinction between northern and southern East Asian populations at genetic markers across the genome. With the confirmation of an African origin for East Asian populations and the observation of a dominating impact of the gene flow entering East Asia from the south in early human settlement, interpretation of the north-south division in this context poses the challenge to the field. Other areas of interest that have been studied include the gene flow between East Asia and its neighbouring regions (i.e. Central Asia, the Sub-continent, America and the Pacific Islands), the origin of Sino-Tibetan populations and expansion of the Chinese.

The Himalayas as a directional barrier to gene flow

High-resolution Y-chromosome haplogroup analyses coupled with Y-short tandem repeat (STR) haplotypes were used to (1) investigate the genetic affinities of three populations from Nepal--including Newar, Tamang, and people from cosmopolitan Kathmandu (referred to as "Kathmandu" subsequently)--as well as a collection from Tibet and (2) evaluate whether the Himalayan mountain range represents a geographic barrier for gene flow between the Tibetan plateau and the South Asian subcontinent. The results suggest that the Tibetans and Nepalese are in part descendants of Tibeto-Burman-speaking groups originating from Northeast Asia. All four populations are represented predominantly by haplogroup O3a5-M134-derived chromosomes, whose Y-STR-based age (+/-SE) was estimated at 8.1+/-2.9 thousand years ago (KYA), more recent than its Southeast Asian counterpart. The most pronounced difference between the two regions is reflected in the opposing high-frequency distributions of haplogroups D in Tibet and R in Nepal. With the exception of Tamang, both Newar and Kathmandu exhibit considerable similarities to the Indian Y-haplogroup distribution, particularly in their haplogroup R and H composition. These results indicate gene flow from the Indian subcontinent and, in the case of haplogroup R, from Eurasia as well, a conclusion that is also supported by the admixture analysis. In contrast, whereas haplogroup D is completely absent in Nepal, it accounts for 50.6% of the Tibetan Y-chromosome gene pool. Coalescent analyses suggest that the expansion of haplogroup D derivatives--namely, D1-M15 and D3-P47 in Tibet--involved two different demographic events (5.1+/-1.8 and 11.3+/-3.7 KYA, respectively) that are more recent than those of D2-M55 representatives common in Japan. Low frequencies, relative to Nepal, of haplogroup J and R lineages in Tibet are also consistent with restricted gene flow from the subcontinent. Yet the presence of haplogroup O3a5-M134 representatives in Nepal indicates that the Himalayas have been permeable to dispersals from the east. These genetic patterns suggest that this cordillera has been a biased bidirectional barrier.

Y-chromosome evidence suggests a common paternal heritage of Austro-Asiatic populations

Background

The Austro-Asiatic linguistic family, which is considered to be the oldest of all the families in India, has a substantial presence in Southeast Asia. However, the possibility of any genetic link among the linguistic sub-families of the Indian Austro-Asiatics on the one hand and between the Indian and the Southeast Asian Austro-Asiatics on the other has not been explored till now. Therefore, to trace the origin and historic expansion of Austro-Asiatic groups of India, we analysed Y-chromosome SNP and STR data of the 1222 individuals from 25 Indian populations, covering all the three branches of Austro-Asiatic tribes, viz. Mundari, Khasi-Khmuic and Mon-Khmer, along with the previously published data on 214 relevant populations from Asia and Oceania.

Results

Our results suggest a strong paternal genetic link, not only among the subgroups of Indian Austro-Asiatic populations but also with those of Southeast Asia. However, maternal link based on mtDNA is not evident. The results also indicate that the haplogroup O-M95 had originated in the Indian Austro-Asiatic populations ~65,000 yrs BP (95% C.I. 25,442 – 132,230) and their ancestors carried it further to Southeast Asia via the Northeast Indian corridor. Subsequently, in the process of expansion, the Mon-Khmer populations from Southeast Asia seem to have migrated and colonized Andaman and Nicobar Islands at a much later point of time.

Conclusion

Our findings are consistent with the linguistic evidence, which suggests that the linguistic ancestors of the Austro-Asiatic populations have originated in India and then migrated to Southeast Asia.

Allelic distribution of HLA class I genes in the Tibetan ethnic population of China

Tibetans live in Qinghai-Tibet Plateau rising about 4000 m a.s.l. in south-west China. Archaeological evidences suggested that there have been humans living in Tibet at least 5000 years ago. However, Tibetan earlier history remains elusive. In the present study, allelic distribution of human leucocyte antigen (HLA)-A, -B and -Cw in 158 unrelated Tibetan Chinese was investigated using sequencing-based typing methods, and a total of 25 HLA-A, 45 HLA-B and 20 HLA-Cw alleles were identified. A*24G1 (27.2%), B*51G1 (16.8%), Cw*04G1 (13.3%) and Cw*070201G1 (13.3%) are the most common HLA-A, -B and -Cw alleles. The most frequently detected haplotypes were A*24G1-B*51G1-Cw*140201 (3.6%), A*24G1-B*51G1 (6.8%), A*02G1-Cw*070201G1 (6.5%) and B*51G1-Cw*140201 (5.0%). Chi-squared test suggested that all three loci fitted the Hardy-Weinberg expectations. No evidence for a departure from selective neutrality at the HLA-A and -B loci was observed. However, significant departure of the observed homozygosity from the expected values was found for HLA-Cw. Though the contemporary Tibetans inhabit the south-west China, Nei's genetic distance measure based on frequencies of HLA-A, -B and -Cw indicated that Tibetans were closer to northern Han Chinese, Mongolian Chinese, Koreans and Japanese rather than to southern Han Chinese. The corresponding dendrogram constructed according to the neighbour-joining method supported that Tibetans separated from southern Han and located in North-East Asian cluster which included northern Han Chinese and Mongolian Chinese. These data were in good agreement with language classification and with a recent hypothesis that Tibetan might originate from northern China along Yellow river.

Y-chromosome evidence of southern origin of the East Asian-specific haplogroup O3-M122

The prehistoric peopling of East Asia by modern humans remains controversial with respect to early population migrations. Here, we present a systematic sampling and genetic screening of an East Asian-specific Y-chromosome haplogroup (O3-M122) in 2,332 individuals from diverse East Asian populations. Our results indicate that the O3-M122 lineage is dominant in East Asian populations, with an average frequency of 44.3%. The microsatellite data show that the O3-M122 haplotypes in southern East Asia are more diverse than those in northern East Asia, suggesting a southern origin of the O3-M122 mutation. It was estimated that the early northward migration of the O3-M122 lineages in East Asia occurred approximately 25,000-30,000 years ago, consistent with the fossil records of modern humans in East Asia.

Analyses of genetic structure of Tibeto-Burman populations reveals sex-biased admixture in southern Tibeto-Burmans

An unequal contribution of male and female lineages from parental populations to admixed ones is not uncommon in the American continents, as a consequence of directional gene flow from European men into African and Hispanic Americans in the past several centuries. However, little is known about sex-biased admixture in East Asia, where substantial migrations are recorded. Tibeto-Burman (TB) populations were historically derived from ancient tribes of northwestern China and subsequently moved to the south, where they admixed with the southern natives during the past 2600 years. They are currently extensively distributed in China and Southeast Asia. In this study, we analyze the variations of 965 Y chromosomes and 754 mtDNAs in >20 TB populations from China. By examining the haplotype group distributions of Y-chromosome and mtDNA markers and their principal components, we show that the genetic structure of the extant southern Tibeto-Burman (STB) populations were primarily formed by two parental groups: northern immigrants and native southerners. Furthermore, the admixture has a bias between male and female lineages, with a stronger influence of northern immigrants on the male lineages (approximately 62%) and with the southern natives contributing more extensively to the female lineages (approximately 56%) in the extant STBs. This is the first genetic evidence revealing sex-biased admixture in STB populations, which has genetic, historical, and anthropological implications.

Summary: The Science of Genealogy by Genetics

This summary lays out the basic science and methodology used in genetic testing that investigates historical population migrations and the ancestry of living individuals. The genetic markers used in this testing, and the distinction between Y-chromosome, mitochondrial and autosomes analysis, are explained and the shortcomings of these methodologies are explored.

Rare Deep-Rooting Y Chromosome Lineages in Humans: Lessons for Phylogeography

There has been considerable debate on the geographic origin of the human Y chromosome Alu polymorphism (YAP). Here we report a new, very rare deep-rooting haplogroup within the YAP clade, together with data on other deep-rooting YAP clades. The new haplogroup, found so far in only five Nigerians, is the least-derived YAP haplogroup according to currently known binary markers. However, because the interior branching order of the Y chromosome genealogical tree remains unknown, it is impossible to impute the origin of the YAP clade with certainty. We discuss the problems presented by rare deep-rooting lineages for Y chromosome phylogeography.

The human Y chromosome: an evolutionary marker comes of age

Until recently, the Y chromosome seemed to fulfil the role of juvenile delinquent among human chromosomes--rich in junk, poor in useful attributes, reluctant to socialize with its neighbours and with an inescapable tendency to degenerate. The availability of the near-complete chromosome sequence, plus many new polymorphisms, a highly resolved phylogeny and insights into its mutation processes, now provide new avenues for investigating human evolution. Y-chromosome research is growing up.

Genetic affinities of the Andaman Islanders, a vanishing human population

BACKGROUND

The Andaman Islands in the Bay of Bengal are inhabited by hunter-gatherers of unknown origin, now on the verge of extinction. The Andamanese and other Asian small-statured peoples, traditionally known as "Negritos," resemble African pygmies. However, it is generally believed that they descend from the early Australo-Melanesian settlers of Southeast Asia and that their resemblance to some Africans is due to adaptation to a similar environment, rather than shared origins.

RESULTS

We analyzed mitochondrial DNA (mtDNA) sequences and RFLP polymorphisms, and Y chromosome biallelic markers and microsatellites, in present-day Andamanese of the Onge, Jarawa, and Great Andamanese tribes, and of inhabitants of the neighboring Nicobar Islands. We also analyzed mtDNA sequences from Andamanese hair samples collected by an ethnographer during 1906-1908. Living Andamanese exhibit low genetic variability that is consistent with their small population size and reproductive isolation.

CONCLUSIONS

Our data indicate that the Andamanese have closer affinities to Asian than to African populations and suggest that they are the descendants of the early Palaeolithic colonizers of Southeast Asia. In contrast, the Nicobarese have genetic affinities to groups widely distributed throughout Asia today, presumably descended from Neolithic agriculturalists.

Resisting a genetic identity: the black Seminoles and genetic tests of ancestry

In July 2000, the Seminole Nation of Oklahoma passed a resolution that would effectively expel a significant portion of its tribal members. The resolution amended the Nation's constitution by changing its membership criteria. Previously, potential members needed to show descent from an enrollee of the 1906 Dawes Rolls, the official American Indian tribal rolls established by the Dawes Commission to facilitate the allotment of reservation land. The amended constitution requires possession of one-eighth Seminole Indian blood, a requirement that a significant portion of the tribe's membership cannot fulfill. The members of the Nation who fail to meet this new membership criterion all have one thing in common: they are black.

Descendents of former slaves who came to live among the Seminole Indians of Florida in the seventeenth and eighteenth centuries, the black Seminoles have been officially recognized by the U.S. government as members of the Seminole Nation of Oklahoma since 1866.

Paternal population history of East Asia: sources, patterns, and microevolutionary processes

Asia has served as a focal point for human migration during much of the Late Pleistocene and Holocene. Clarification of East Asia's role as a source and/or transit point for human dispersals requires that this region's own settlement history be understood. To this end, we examined variation at 52 polymorphic sites on the nonrecombining portion of the Y chromosome (NRY) in 1,383 unrelated males, representing 25 populations from southern East Asia (SEAS), northern East Asia (NEAS), and central Asia (CAS). The polymorphisms defined 45 global haplogroups, 28 of which were present in these three regions. Although heterozygosity levels were similar in all three regions, the average pairwise difference among haplogroups was noticeably smaller in SEAS. Multidimensional scaling analysis indicated a general separation of SEAS versus NEAS and CAS populations, and analysis of molecular variance produced very different values of Phi(ST) in NEAS and SEAS populations. In spatial autocorrelation analyses, the overall correlogram exhibited a clinal pattern; however, the NEAS populations showed evidence of both isolation by distance and ancient clines, whereas there was no evidence of structure in SEAS populations. Nested cladistic analysis demonstrated that population history events and ongoing demographic processes both contributed to the contrasting patterns of NRY variation in NEAS and SEAS. We conclude that the peopling of East Asia was more complex than earlier models had proposed-that is, a multilayered, multidirectional, and multidisciplinary framework is necessary. For instance, in addition to the previously recognized genetic and dental dispersal signals from SEAS to NEAS populations, CAS has made a significant contribution to the contemporary gene pool of NEAS, and the Sino-Tibetan expansion has left traces of a genetic trail from northern to southern China.

Y chromosome haplotypes reveal prehistorical migrations to the Himalayas

By using 19 Y chromosome biallelic markers and 3 Y chromosome microsatellite markers, we analyzed the genetic structure of 31 indigenous Sino-Tibetan speaking populations (607 individuals) currently residing in East, Southeast, and South Asia. Our results showed that a T to C mutation at locus M122 is highly prevalent in almost all of the Sino-Tibetan populations, implying a strong genetic affinity among populations in the same language family. Furthermore, the extremely high frequency of H8, a haplotype derived from M122C, in the Sino-Tibetan speaking populations in the Himalayas including Tibet and northeast India indicated a strong bottleneck effect that occurred during a westward and then southward migration of the founding population of Tibeto-Burmans. We, therefore, postulate that the ancient people, who lived in the upper-middle Yellow River basin about 10,000 years ago and developed one of the earliest Neolithic cultures in East Asia, were the ancestors of modern Sino-Tibetan populations.

Natives or immigrants: modern human origin in east Asia

East Asia is one of the few regions in the world where a relatively large number of human fossils have been unearthed--a discovery that has been taken as evidence for an independent local origin of modern humans outside of Africa. However, genetic studies conducted in the past ten years, especially using Y chromosomes, have provided unequivocal evidence for an African origin of East Asian populations. The genetic signatures present in diverse East Asian populations mark the footsteps of prehistoric migrations that occurred tens of thousands of years ago.

Melanesian origin of Polynesian Y chromosomes

BACKGROUND

Two competing hypotheses for the origins of Polynesians are the 'express-train' model, which supposes a recent and rapid expansion of Polynesian ancestors from Asia/Taiwan via coastal and island Melanesia, and the 'entangled-bank' model, which supposes a long history of cultural and genetic interactions among Southeast Asians, Melanesians and Polynesians. Most genetic data, especially analyses of mitochondrial DNA (mtDNA) variation, support the express-train model, as does linguistic and archaeological evidence. Here, we used Y-chromosome polymorphisms to investigate the origins of Polynesians.

RESULTS

We analysed eight single nucleotide polymorphisms (SNPs) and seven short tandem repeat (STR) loci on the Y chromosome in 28 Cook Islanders from Polynesia and 583 males from 17 Melanesian, Asian and Australian populations. We found that all Polynesians belong to just three Y-chromosome haplotypes, as defined by unique event polymorphisms. The major Y haplotype in Polynesians (82% frequency) was restricted to Melanesia and eastern Indonesia and most probably arose in Melanesia. Coalescence analysis of associated Y-STR haplotypes showed evidence of a population expansion in Polynesians, beginning about 2,200 years ago. The other two Polynesian Y haplotypes were widespread in Asia but were also found in Melanesia.

CONCLUSIONS

All Polynesian Y chromosomes can be traced back to Melanesia, although some of these Y-chromosome types originated in Asia. Together with other genetic and cultural evidence, we propose a new model of Polynesian origins that we call the 'slow-boat' model: Polynesian ancestors did originate from Asia/Taiwan but did not move rapidly through Melanesia; rather, they interacted with and mixed extensively with Melanesians, leaving behind their genes and incorporating many Melanesian genes before colonising the Pacific.