Biology subjects

Brigitte Pakendorf

Publications and source records attributed to Brigitte Pakendorf.

3 recordsLinked to original sources

bioRxiv2015

Refining the Y chromosome phylogeny with southern African sequences

The recent availability of large-scale sequence data for the human Y chromosome has revolutionized analyses of and insights gained from this non-recombining, paternally inherited chromosome. However, the studies to date focus on Eurasian variation, and hence the diversity of early-diverging branches found in Africa has not been adequately documented. Here we analyze over 900 kb of Y chromosome sequence obtained from 547 individuals from southern African Khoisan and Bantuspeaking populations, identifying 232 new sequences from basal haplogroups A and B. We find new branches within haplogroups A2 and A3b1 and suggest that the prehistory of haplogroup B2a is more complex than previously suspected; this haplogroup is likely to have existed in Khoisan groups before the arrival of Bantu-speakers, who brought additional B2a lineages to southern Africa. Furthermore, we estimate older dates than obtained previously for both the A2-T node within the human Y chromosome phylogeny and for some individual haplogroups. Finally, there is pronounced variation in branch length between major haplogroups; haplogroups associated with Bantu-speakers have significantly longer branches. This likely reflects a combination of biases in the SNP calling process and demographic factors, such as an older average paternal age (hence a higher mutation rate), a higher effective population size, and/or a stronger effect of population expansion for Bantu-speakers than for Khoisan groups.

Evolutionary Biology↗

bioRxiv2015

The complex admixture history and recent southern origins of Siberian populations

Although Siberia was inhabited by modern humans at an early stage, there is still debate over whether this area remained habitable during the extremely cold period of the Last Glacial Maximum or whether it was subsequently repopulated by peoples with a recent shared ancestry. Previous studies of the genetic history of Siberian populations were hampered by the extensive admixture that appears to have taken place among these populations, since commonly used methods assume a tree-like population history and at most single admixture events. We therefore developed a new method based on the covariance of ancestry components, which we validated with simulated data, in order to investigate this potentially complex admixture history and to distinguish the effects of shared ancestry from prehistoric migrations and contact. We furthermore adapted a previously devised method of admixture dating for use with multiple events of gene flow, and applied these methods to whole-genome genotype data from over 500 individuals belonging to 20 different Siberian ethnolinguistic groups. The results of these analyses indicate that there have indeed been multiple layers of admixture detectable in most of the Siberian populations, with considerable differences in the admixture histories of individual populations, and with the earliest events dated to not more than 4500 years ago. Furthermore, most of the populations of Siberia included here, even those settled far to the north, can be shown to have a southern origin. These results provide support for a recent population replacement in this region, with the northward expansions of different populations possibly being driven partly by the advent of pastoralism, especially reindeer domestication. These newly developed methods to analyse multiple admixture events should aid in the investigation of similarly complex population histories elsewhere.\n\nAuthor SummaryWe developed a new method that lets us disentangle complex admixture events and date the individual episodes of gene flow. We applied this method to a large dataset of genome-wide SNP genotypes from a linguistically diverse sample of populations covering the extent of Siberia. Our results demonstrate that these populations have been in intense contact with each other, with most of them carrying more than two, and up to six different ancestries. Nevertheless, as shown by the dates we estimate, these various admixture events have taken place over a relatively short time, with the oldest dating to not more than 4500 years ago. Our results emphasize the enormous impact that contact has had on the genetic history of these Siberian populations, and the methods developed here will be of use in the investigation of admixture events in populations around the world.

Genetics↗

bioRxiv2014

Migration and interaction in a contact zone: mtDNA variation among Bantu-speakers in southern Africa

Bantu speech communities expanded over large parts of sub-Saharan Africa within the last 4000-5000 years, reaching different parts of southern Africa 1200-2000 years ago. The Bantu languages subdivide in several major branches, with languages belonging to the Eastern and Western Bantu branches spreading over large parts of Central, Eastern, and Southern Africa. There is still debate whether this linguistic divide is correlated with a genetic distinction between Eastern and Western Bantu speakers. During their expansion, Bantu speakers would have come into contact with diverse local populations, such as the Khoisan hunter-gatherers and pastoralists of southern Africa, with whom they may have intermarried. In this study, we analyze complete mtDNA genome sequences from over 900 Bantu-speaking individuals from Angola, Zambia, Namibia, and Botswana to investigate the demographic processes at play during the last stages of the Bantu expansion. Our results show that most of these Bantu-speaking populations are genetically very homogenous, with no genetic division between speakers of Eastern and Western Bantu languages. Most of the mtDNA diversity in our dataset is due to different degrees of admixture with autochthonous populations. Only the pastoralist Himba and Herero stand out due to high frequencies of particular L3f and L3d lineages; the latter are also found in the neighboring Damara, who speak a Khoisan language and were foragers and small-stock herders. In contrast, the close cultural and linguistic relatives of the Herero and Himba, the Kuvale, are genetically similar to other Bantu-speakers. Nevertheless, as demonstrated by resampling tests, the genetic divergence of Herero, Himba, and Kuvale is compatible with a common shared ancestry with high levels of drift and differential female admixture with local pre-Bantu populations.

Evolutionary Biology↗