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Summary: Male-Driven Biased Gene Conversion Governs the Evolution of Base
Composition in Human Alu Repeats
Matthew T. Webster,* Nick G. C. Smith, Lina Hultin-Rosenberg,*
Peter F. Arndt,à and Hans Ellegren*
*Department of Evolution, Genomics and Systematics, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden;
Department of Mathematics and Statistics, Lancaster University, Lancaster, United Kingdom; and àMax Planck Institute for
Molecular Genetics, Berlin, Germany
Regional biases in substitution pattern are likely to be responsible for the large-scale variation in base composition
observed in vertebrate genomes. However, the evolutionary forces responsible for these biases are still not clearly defined.
In order to study the processes of mutation and fixation across the entire human genome, we analyzed patterns of sub-
stitution in Alu repeats since their insertion. We also studied patterns of human polymorphism within the repeats. There is a
highly significant effect of recombination rate on the pattern of substitution, whereas no such effect is seen on the pattern of
polymorphism. These results suggest that regional biases in substitution are caused by biased gene conversion, a process
that increases the probability of fixation of mutations that increase GC content. Furthermore, the strongest correlate of
substitution patterns is found to be male recombination rates rather than female or sex-averaged recombination rates. This
indicates that in addition to sexual dimorphism in recombination rates, the sexes also differ in the relative rates of crossover
and gene conversion.
Introduction
The causes and significance of the large-scale varia-
tion in base composition (GC content) observed in verte-
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