Silke Brauer

Characteristics and frequency of germline mutations at microsatellite loci from the human Y chromosome, as revealed by direct observation in father/son pairs.

A number of applications of analysis of human Y-chromosome microsatellite loci to human evolution and forensic science require reliable estimates of the mutation rate and knowledge of the mutational mechanism. We therefore screened a total of 4,999 meioses from father/son pairs with confirmed paternity (probability >/=99. 9%) at 15 Y-chromosomal microsatellite loci and identified 14 mutations. The locus-specific mutation-rate estimates were 0-8. 58x10-3, and the average mutation rate estimates were 3.17x10-3 (95% confidence interval [CI] 1.89-4.94x10-3) across 8 tetranucleotide microsatellites and 2.80x10-3 (95% CI 1.72-4.27x10-3) across all 15 Y-chromosomal microsatellites studied. Our data show a mutational bias toward length increase, on the basis of observation of more repeat gains than losses (10:4). The data are in almost complete agreement with the stepwise-mutation model, with 13 single-repeat changes and 1 double-repeat change. Sequence analysis revealed that all mutations occurred in uninterrupted homogenous arrays of >/=11 repeats. We conclude that mutation rates and characteristics of human Y-chromosomal microsatellites are consistent with those of autosomal microsatellites. This indicates that the general mutational mechanism of microsatellites is independent of recombination.

Reduced Y-chromosome, but not mitochondrial DNA, diversity in human populations from West New Guinea.

To investigate the paternal population history of New Guinea, 183 individuals from 11 regional populations of West New Guinea (WNG) and 131 individuals from Papua New Guinea (PNG) were analyzed at 26 binary markers and seven short-tandem-repeat loci from the nonrecombining part of the human Y chromosome and were compared with 14 populations of eastern and southeastern Asia, Polynesia, and Australia. Y-chromosomal diversity was low in WNG compared with PNG and with most other populations from Asia/Oceania; a single haplogroup (M-M4) accounts for 75% of WNG Y chromosomes, and many WNG populations have just one Y haplogroup. Four Y-chromosomal lineages (haplogroups M-M4, C-M208, C-M38, and K-M230) account for 94% of WNG Y chromosomes and 78% of all Melanesian Y chromosomes and were identified to have most likely arisen in Melanesia. Haplogroup C-M208, which in WNG is restricted to the Dani and Lani, two linguistically closely related populations from the central and western highlands of WNG, was identified as the major Polynesian Y-chromosome lineage. A network analysis of associated Y-chromosomal short-tandem-repeat haplotypes suggests two distinct population expansions involving C-M208--one in New Guinea and one in Polynesia. The observed low levels of Y-chromosome diversity in WNG contrast with high levels of mtDNA diversity reported for the same populations. This most likely reflects extreme patrilocality and/or biased male reproductive success (polygyny). Our data further provide evidence for primarily female-mediated gene flow within the highlands of New Guinea but primarily male-mediated gene flow between highland and lowland/coastal regions.

Independent histories of human y chromosomes from melanesia and Australia

To investigate the origins and relationships of Australian and Melanesian populations, 611 males from 18 populations from Australia, Melanesia, and eastern/southeastern Asia were typed for eight single-nucleotide polymorphism (SNP) loci and seven short tandem-repeat loci on the Y chromosome. A unique haplotype, DYS390.1del/RPS4Y711T, was found at a frequency of 53%-69% in Australian populations, whereas the major haplotypes found in Melanesian populations (M4G/M5T/M9G and DYS390.3del/RPS4Y711T) are absent from the Australian populations. The Y-chromosome data thus indicate independent histories for Australians and Melanesians, a finding that is in agreement with evidence from mtDNA but that contradicts some analyses of autosomal loci, which show a close relationship between Australian and Melanesian (specifically, highland Papua New Guinean) populations. Since the Australian and New Guinean landmasses were connected when first colonized by humans > or =50,000 years ago but separated some 8,000 years ago, a possible way to reconcile all the genetic data is to infer that the Y-chromosome and mtDNA results reflect the past 8,000 years of independent history for Australia and New Guinea, whereas the autosomal loci reflect the long preceding period of common origin and shared history. Two Y-chromosome haplotypes (M119C/M9G and M122C/M9G) that originated in eastern/southeastern Asia are present in coastal and island Melanesia but are rare or absent in both Australia and highland Papua New Guinea. This distribution, along with demographic analyses indicating that population expansions for both haplotypes began approximately 4,000-6,000 years ago, suggests that these haplotypes were brought to Melanesia by the Austronesian expansion. Most of the populations in this study were previously typed for mtDNA SNPs; population differentiation is greater for the Y chromosome than for mtDNA and is significantly correlated with geographic distance, a finding in agreement with results of similar analyses of European populations.

Demographic history of Oceania inferred from genome-wide data

BACKGROUND The human history of Oceania comprises two extremes: the initial colonizations of Near Oceania, one of the oldest out-of-Africa migrations, and of Remote Oceania, the most recent expansion into unoccupied territories. Genetic studies, mostly using uniparentally inherited DNA, have shed some light on human origins in Oceania, particularly indicating that Polynesians are of mixed East Asian and Near Oceanian ancestry. Here, we use ∼1 million single nucleotide polymorphisms (SNPs) to investigate the demographic history of Oceania in a more detailed manner. RESULTS We developed a new approach to account for SNP ascertainment bias, used approximate Bayesian computation simulations to choose the best-fitting model of population history, and estimated demographic parameters. We find that the ancestors of Near Oceanians diverged from ancestral Eurasians ∼27 thousand years ago (kya), suggesting separate initial occupations of both territories. The genetic admixture in Polynesian history between East Asians (∼87%) and Near Oceanians (∼13%) occurred ∼3 kya, prior to the colonization of Polynesia. Fijians are of Polynesian (∼65%) and additional Near Oceanian (∼35%) ancestry not found in Polynesians, with this admixture occurring considerably after the initial settlement of Remote Oceania. Our data support a greater contribution of East Asian women than men in the admixture history of Remote Oceania and highlight population substructure in Polynesia and New Guinea. CONCLUSIONS Despite the inherent ascertainment bias, genome-wide SNP data provide new insights into the genetic history of Oceana. Our approach to correct for ascertainment bias and obtain reliable inferences concerning demographic history should prove useful in other such studies.

Genome-wide Analysis Indicates More Asian than Melanesian Ancestry of Polynesians

Analyses of mitochondrial DNA (mtDNA) and nonrecombining Y chromosome (NRY) variation in the same populations are sometimes concordant but sometimes discordant. Perhaps the most dramatic example known of the latter concerns Polynesians, in which about 94% of Polynesian mtDNAs are of East Asian origin, while about 66% of Polynesian Y chromosomes are of Melanesian origin. Here we analyze on a genome-wide scale, to our knowledge for the first time, the origins of the autosomal gene pool of Polynesians by screening 377 autosomal short tandem repeat (STR) loci in 47 Pacific Islanders and compare the results with those obtained from 44 Chinese and 24 individuals from Papua New Guinea. Our data indicate that on average about 79% of the Polynesian autosomal gene pool is of East Asian origin and 21% is of Melanesian origin. The genetic data thus suggest a dual origin of Polynesians with a high East Asian but also considerable Melanesian component, reflecting sex-biased admixture in Polynesian history in agreement with the Slow Boat model. More generally, these results also demonstrate that conclusions based solely on uniparental markers, which are frequently used in population history studies, may not accurately reflect the history of the autosomal gene pool of a population.

Genetic admixture history of eastern Indonesia as revealed by Y-chromosome and mitochondrial DNA analysis

Eastern Indonesia possesses more linguistic diversity than any other region in Southeast Asia, with both Austronesian (AN) languages that are of East Asian origin, as well as non-Austronesian (NAN) languages of likely Melanesian origin. Here, we investigated the genetic history of human populations from seven eastern Indonesian islands, including AN and NAN speakers, as well as the relationship between languages and genes, by means of nonrecombining Y-chromosomal (NRY) and mitochondrial DNA (mtDNA) analysis. We found that the eastern Indonesian gene pool consists of East Asian as well as Melanesian components, as might be expected based on linguistic evidence, but also harbors putative indigenous eastern Indonesian signatures that perhaps reflect the initial occupation of the Wallacea by aboriginal hunter-gatherers already in Palaeolithic times. Furthermore, both NRY and mtDNA data showed a complete lack of correlation between linguistic and genetic relationships, most likely reflecting genetic admixture and/or language shift. In addition, we noted a small fraction of the NRY and mtDNA data shared between eastern Indonesians and Australian Aborigines likely reflecting an ancient link between Asia and Australia. Our data thus provide insights into the complex genetic ancestry history of eastern Indonesian islanders characterized by several admixture episodes and demonstrate a clear example of the lack of the often-assumed correlation between the genes and languages of human populations.

Apparent intrachromosomal exchange on the human Y chromosome explained by population history

The human Y chromosome displays an unusual content of repetitive sequences. Y-chromosomal repeats are potential targets for intrachromosomal recombination, which is thought to be involved in a number of Y-associated defects, such as male infertility. Such rearrangements could potentially be investigated by the use of highly polymorphic DNA markers located within the repeat units, such as microsatellites. Here we analyse the two copies of the Y-chromosomal microsatellite DYS385, which we identified and localized to an ∼190 kb duplicated and inverted fragment at Yq11.223. We found a highly significant correlation (r=0.853, P<0.001) and a nonsignificant difference in a χ2-test (χ2=15.45, P>0.05) between the allele frequency distributions at both copies of the Y-STR in a German population sample (n=70). Such nearly identical allele frequency distribution between two copies of a duplicated highly polymorphic microsatellite cannot be explained by the independent mutational process that creates microsatellite alleles. Instead, this might be interpreted as evidence for a reciprocal intrachromosomal exchange process between the duplicated fragments. However, more detailed analyses using additional human populations as well as additional Y chromosome markers revealed that this phenomenon is highly population-specific and disappears completely when Y-STR diversity is analysed in association with two Y-SNP haplogroups. We found that the diversity of the two DYS385 loci (and other Y-STRs) is highly depending on the haplogroup background, and that equal proportions of both haplogroups in the German sample explains the nearly identical allele frequency distributions at the two DYS385 loci. Thus, we demonstrate here that allele frequency distributions at duplicate loci that are suggestive of intrachromosomal recombination can be explained solely by population history.

Online Y-chromosomal short tandem repeat haplotype reference database (YHRD) for U.S. populations.

We describe here an online Y-chromosomal short tandem repeat haplotype reference database (YHRD) for U.S. populations, which represents 9-locus Y-STR haplotypes for 1705 African-Americans, European-Americans and Hispanics as of October 2001. This database is available online (http://www.ystr. org/usa/), free to access and was generated in order to supply the U.S. forensic DNA community with a valuable resource for frequencies of complete or incomplete 9-locus Y-STR haplotypes, as well as information about typing protocols and population genetic analyses. Pairwise R(ST)-statistics derived from the Y-STR haplotypes indicate no significant substructure among African-American populations from different regions of the U.S., nor (usually) among European-American and Hispanic populations. Thus, pooling of Y-STR haplotype data from regional populations within these three major groups is appropriate in order to obtain larger sample sizes. However, pooling of different major populations is generally not recommended due to statistically significant differences between African-American populations and all European-American/Hispanic populations, as well as between some European-American and Hispanic populations.

Clinal distribution of human genomic diversity across the Netherlands despite archaeological evidence for genetic discontinuities in Dutch population history

BackgroundThe presence of a southeast to northwest gradient across Europe in human genetic diversity is a well-established observation and has recently been confirmed by genome-wide single nucleotide polymorphism (SNP) data. This pattern is traditionally explained by major prehistoric human migration events in Palaeolithic and Neolithic times. Here, we investigate whether (similar) spatial patterns in human genomic diversity also occur on a micro-geographic scale within Europe, such as in the Netherlands, and if so, whether these patterns could also be explained by more recent demographic events, such as those that occurred in Dutch population history.MethodsWe newly collected data on a total of 999 Dutch individuals sampled at 54 sites across the country at 443,816 autosomal SNPs using the Genome-Wide Human SNP Array 5.0 (Affymetrix). We studied the individual genetic relationships by means of classical multidimensional scaling (MDS) using different genetic distance matrices, spatial ancestry analysis (SPA), and ADMIXTURE software. We further performed dedicated analyses to search for spatial patterns in the genomic variation and conducted simulations (SPLATCHE2) to provide a historical interpretation of the observed spatial patterns.ResultsWe detected a subtle but clearly noticeable genomic population substructure in the Dutch population, allowing differentiation of a north-eastern, central-western, central-northern and a southern group. Furthermore, we observed a statistically significant southeast to northwest cline in the distribution of genomic diversity across the Netherlands, similar to earlier findings from across Europe. Simulation analyses indicate that this genomic gradient could similarly be caused by ancient as well as by the more recent events in Dutch history.ConclusionsConsidering the strong archaeological evidence for genetic discontinuity in the Netherlands, we interpret the observed clinal pattern of genomic diversity as being caused by recent rather than ancient events in Dutch population history. We therefore suggest that future human population genetic studies pay more attention to recent demographic history in interpreting genetic clines. Furthermore, our study demonstrates that genetic population substructure is detectable on a small geographic scale in Europe despite recent demographic events, a finding we consider potentially relevant for future epidemiological and forensic studies.

Human genetics of the Kula Ring: Y-chromosome and mitochondrial DNA variation in the Massim of Papua New Guinea

The island region at the southeastern-most tip of New Guinea and its inhabitants known as Massim are well known for a unique traditional inter-island trading system, called Kula or Kula Ring. To characterize the Massim genetically, and to evaluate the influence of the Kula Ring on patterns of human genetic variation, we analyzed paternally inherited Y-chromosome (NRY) and maternally inherited mitochondrial (mt) DNA polymorphisms in >400 individuals from this region. We found that the nearly exclusively Austronesian-speaking Massim people harbor genetic ancestry components of both Asian (AS) and Near Oceanian (NO) origin, with a proportionally larger NO NRY component versus a larger AS mtDNA component. This is similar to previous observations in other Austronesian-speaking populations from Near and Remote Oceania and suggests sex-biased genetic admixture between Asians and Near Oceanians before the occupation of Remote Oceania, in line with the Slow Boat from Asia hypothesis on the expansion of Austronesians into the Pacific. Contrary to linguistic expectations, Rossel Islanders, the only Papuan speakers of the Massim, showed a lower amount of NO genetic ancestry than their Austronesian-speaking Massim neighbors. For the islands traditionally involved in the Kula Ring, a significant correlation between inter-island travelling distances and genetic distances was observed for mtDNA, but not for NRY, suggesting more male- than female-mediated gene flow. As traditionally only males take part in the Kula voyages, this finding may indicate a genetic signature of the Kula Ring, serving as another example of how cultural tradition has shaped human genetic diversity.