Biology subjects

Kelso, J.

Publications and source records attributed to Kelso, J..

4 recordsLinked to original sources

bioRxiv2018

The limits of long-term selection against Neandertal introgression

Several studies have suggested that introgressed Neandertal DNA was subjected to negative selection in modern humans due to deleterious alleles that had accumulated in the Neandertals after they split from the modern human lineage. A striking observation in support of this is an apparent monotonic decline in Neandertal ancestry observed in modern humans in Europe over the past 45 thousand years. Here we show that this apparent decline is an artifact caused by gene flow between West Eurasians and Africans, which is not taken into account by statistics previously used to estimate Neandertal ancestry. When applying a more robust statistic that takes advantage of two high-coverage Neandertal genomes, we find no evidence for a change in Neandertal ancestry in Western Europe over the past 45 thousand years. We use whole-genome simulations of selection and introgression to investigate a wide range of model parameters, and find that negative selection is not expected to cause a significant long-term decline in genome-wide Neandertal ancestry. Nevertheless, these models recapitulate previously observed signals of selection against Neandertal alleles, in particular a depletion of Neandertal ancestry in conserved genomic regions that are likely to be of functional importance. Thus, we find that negative selection against Neandertal ancestry has not played as strong a role in recent human evolution as had previously been assumed.

evolutionary biology↗

bioRxiv2018

Immune gene diversity in archaic and present-day humans

Genome-wide analyses of two Neandertals and a Denisovan have shown that these archaic humans had lower genetic heterozygosity than present-day people. A similar reduction in genetic diversity of protein-coding genes (gene diversity) was found in exome sequences of three Neandertals. Reduced gene diversity, and particularly in genes involved in immunity, may have important functional consequences. In fact, it has been suggested that reduced diversity in immune genes may have contributed to Neandertal extinction. We therefore explored gene diversity in different human groups and at different time points on the Neandertal lineage with a particular focus on the diversity of genes involved in innate immunity and genes of the Major Histocompatibility Complex (MHC).\n\nWe find that the two Neandertals and the Denisovan have similar gene diversity, both significantly lower than any present-day human. This is true across gene categories, with no gene set showing an excess decrease in diversity compared to the genome-wide average. Innate immune-related genes show a similar reduction in diversity to other genes, both in present-day and archaic humans. There is also no observable decrease in gene diversity over time in Neandertals, suggesting that there may have been no ongoing reduction in gene diversity in later Neandertals, although this needs confirmation with a larger sample size. In both archaic and present-day humans, genes with the highest levels of diversity are enriched for MHC-related functions. In fact, in archaic humans the MHC genes show evidence of having retained more diversity than genes involved only in the innate immune system.

genetics↗

bioRxiv2018

Human stem cell resources are an inroad to Neandertal DNA functions

Pluripotent stem cells from diverse humans offer the potential to study human functional variation in controlled culture environments. A portion of this variation originates from ancient admixture between modern humans and Neandertals, which introduced alleles that left a phenotypic legacy on individual humans today. Here we show that a large repository of human induced pluripotent stem cells (iPSCs) harbors extensive Neandertal DNA, including most known functionally relevant Neandertal alleles present in modern humans. This resource contains Neandertal DNA that contributes to human phenotypes and diseases, encodes hundreds of amino acid changes, and alters gene expression in specific tissues. Human iPSCs thus provide an opportunity to experimentally explore the Neandertal contribution to present-day phenotypes, and potentially study Neandertal traits.

evolutionary biology↗

bioRxiv2018

Ancient Fennoscandian genomes reveal origin and spread of Siberian ancestry in Europe

European history has been shaped by migrations of people, and their subsequent admixture. Recently, evidence from ancient DNA has brought new insights into migration events that could be linked to the advent of agriculture, and possibly to the spread of Indo-European languages. However, little is known so far about the ancient population history of north-eastern Europe, in particular about populations speaking Uralic languages, such as Finns and Saami. Here we analyse ancient genomic data from 11 individuals from Finland and Northwest Russia. We show that the specific genetic makeup of northern Europe traces back to migrations from Siberia that began at least 3,500 years ago. This ancestry was subsequently admixed into many modern populations in the region, in particular populations speaking Uralic languages today. In addition, we show that ancestors of modern Saami inhabited a larger territory during the Iron Age than today, which adds to historical and linguistic evidence for the population history of Finland.

genomics↗