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Copyright McAllister, Evans. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Increased Nucleotide Diversity with Transient Y Linkage in Drosophila americana Department of Biological Sciences and Roy J. Carver Center for Comparative Genomics, University of Iowa, Iowa City, Iowa, United States of America Adam Chippindale, Academic Editor Queens University, Canada * To whom correspondence should be addressed. E-mail: bryant-mcallister/at/uiowa.edu Conceived and designed the experiments: BM. Performed the experiments: AE. Analyzed the data: BM. Contributed reagents/materials/analysis tools: BM. Wrote the paper: BM. Received September 6, 2006; Accepted November 21, 2006. This article has been cited by other articles in PMC.Abstract Recombination shapes nucleotide variation within genomes. Patterns are thought to arise from the local recombination landscape, influencing the degree to which neutral variation experiences hitchhiking with selected variation. This study examines DNA polymorphism along Chromosome 4 (element B) of Drosophila americana to identify effects of hitchhiking arising as a consequence of Y-linked transmission. A centromeric fusion between the X and 4th chromosomes segregates in natural populations of D. americana. Frequency of the X-4 fusion exhibits a strong positive correlation with latitude, which has explicit consequences for unfused 4th chromosomes. Unfused Chromosome 4 exists as a non-recombining Y chromosome or as an autosome proportional to the frequency of the X-4 fusion. Furthermore, Y linkage along the unfused 4 is disrupted as a function of the rate of recombination with the centromere. Inter-population and intra-chromosomal patterns of nucleotide diversity were assayed using six regions distributed along unfused 4th chromosomes derived from populations with different frequencies of the X-4 fusion. No difference in overall level of nucleotide diversity was detected among populations, yet variation along the chromosome exhibits a distinct pattern in relation to the X-4 fusion. Sequence diversity is inflated at loci experiencing the strongest Y linkage. These findings are inconsistent with the expected reduction in nucleotide diversity resulting from hitchhiking due to background selection or selective sweeps. In contrast, excessive polymorphism is accruing in association with transient Y linkage, and furthermore, hitchhiking with sexually antagonistic alleles is potentially responsible. |
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