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Zhu, Qihui

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Zhu

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Qihui

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Zhu, Qihui
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    Balancing Selection on a Regulatory Region Exhibiting Ancient Variation That Predates Human–Neandertal Divergence
    (Public Library of Science, 2013) Gokcumen, Omer; Zhu, Qihui; Mulder, Lubbertus C. F.; Iskow, Rebecca C.; Austermann, Christian; Scharer, Christopher D.; Raj, Towfique; Boss, Jeremy M.; Sunyaev, Shamil; Price, Alkes; Stranger, Barbara; Simon, Viviana; Lee, Charles
    Ancient population structure shaping contemporary genetic variation has been recently appreciated and has important implications regarding our understanding of the structure of modern human genomes. We identified a ∼36-kb DNA segment in the human genome that displays an ancient substructure. The variation at this locus exists primarily as two highly divergent haplogroups. One of these haplogroups (the NE1 haplogroup) aligns with the Neandertal haplotype and contains a 4.6-kb deletion polymorphism in perfect linkage disequilibrium with 12 single nucleotide polymorphisms (SNPs) across diverse populations. The other haplogroup, which does not contain the 4.6-kb deletion, aligns with the chimpanzee haplotype and is likely ancestral. Africans have higher overall pairwise differences with the Neandertal haplotype than Eurasians do for this NE1 locus (p<10−15). Moreover, the nucleotide diversity at this locus is higher in Eurasians than in Africans. These results mimic signatures of recent Neandertal admixture contributing to this locus. However, an in-depth assessment of the variation in this region across multiple populations reveals that African NE1 haplotypes, albeit rare, harbor more sequence variation than NE1 haplotypes found in Europeans, indicating an ancient African origin of this haplogroup and refuting recent Neandertal admixture. Population genetic analyses of the SNPs within each of these haplogroups, along with genome-wide comparisons revealed significant FST (p = 0.00003) and positive Tajima's D (p = 0.00285) statistics, pointing to non-neutral evolution of this locus. The NE1 locus harbors no protein-coding genes, but contains transcribed sequences as well as sequences with putative regulatory function based on bioinformatic predictions and in vitro experiments. We postulate that the variation observed at this locus predates Human–Neandertal divergence and is evolving under balancing selection, especially among European populations.
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    Refinement of Primate Copy Number Variation Hotspots Identifies Candidate Genomic Regions Evolving Under Positive Selection
    (BioMed Central, 2011) Babb, Paul L; Iskow, Rebecca C; Mills, Ryan E; Ionita-Laza, Iuliana; Gokcumen, Omer; Zhu, Qihui; Shi, Xinghua; Vallender, Eric; Clark, Andrew G.; Johnson, Welkin Eric; Lee, Charles
    Background: Copy number variants (CNVs), defined as losses and gains of segments of genomic DNA, are a major source of genomic variation. Results: In this study, we identified over 2,000 human CNVs that overlap with orthologous chimpanzee or orthologous macaque CNVs. Of these, 170 CNVs overlap with both chimpanzee and macaque CNVs, and these were collapsed into 34 hotspot regions of CNV formation. Many of these hotspot regions of CNV formation are functionally relevant, with a bias toward genes involved in immune function, some of which were previously shown to evolve under balancing selection in humans. The genes in these primate CNV formation hotspots have significant differential expression levels between species and show evidence for positive selection, indicating that they have evolved under species-specific, directional selection. Conclusions: These hotspots of primate CNV formation provide a novel perspective on divergence and selective pressures acting on these genomic regions.