Benefits of Sexual Reproduction

http://www.sciencemag.org/cgi/content/abstract/311/5763/990?etoc

Science 17 February 2006:
Vol. 311. no. 5763, pp. 990 - 992
DOI: 10.1126/science.1118152

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Reports
Transitions to Asexuality Result in Excess Amino Acid Substitutions
Susanne Paland and Michael Lynch

Theory predicts that linkage between genetic loci reduces the
efficiency of purifying selection. Because of the permanent linkage of
all heritable genetic material, asexual lineages may be exceptionally
prone to deleterious-mutation accumulation in both nuclear and
organelle genes. Here, we show that the ratio of the rate of amino acid
to silent substitution (Ka/Ks) in mitochondrial protein-coding genes is
higher in obligately asexual lineages than in sexual lineages of the
microcrustacean Daphnia pulex. Using a phylogeny-based approach to
quantify the frequency of mutational-effect classes, we estimate that
mitochondrial protein-coding genes in asexual lineages accumulate
deleterious amino acid substitutions at four times the rate in sexual
lineages. These results support the hypothesis that sexual reproduction
plays a prominent role in reducing the mutational burden in
populations.


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