Showing papers by "Laurence D. Hurst published in 1997"
TL;DR: This hypothesis that selection will often favour a lower mutation rate on the X chromosome than on autosomes, owing to the exposure of deleterious recessive mutations on hemizygous chromosomes is tested by examining 33 X-linked genes that have been sequenced in both mouse and rat, and compared their rate of evolution against 238 autosomal genes.
Abstract: The equilibrium per-genome mutation rate in sexual species is thought to result from a trade-off between the benefits of reducing the deleterious mutation rate and the costs of increasing fidelity1,2. We propose that selection will often favour a lower mutation rate on the X chromosome than on autosomes, owing to the exposure of deleterious recessive mutations on hemizygous chromosomes. We tested this hypothesis by examining 33 X-linked genes that have been sequenced in both mouse and rat, and compared their rate of evolution against 238 autosomal genes. The X-linked genes were found to have a significantly lower rate of synonymous substitution than the autosomal genes. Neither the supposed higher mutation rate in males nor stronger purifying selection against slightly deleterious mutations on the X chromosome can account for the low value. The most parsimonious explanation is that rodents have a lower mutation rate on the X chromosome than on autosomes. It is therefore likely that previous indirect estimates of the excess male mutation rate are inaccurate. Indeed, after correction we find no evidence for a male-biased mutation rate in rodents. Furthermore, the rate of synonymous substitution in Y-linked genes is not significantly different from that in autosomal ones. The extent to which enhanced male mutation rates are problematic3 for the mutational deterministic model4 of the evolution of sex must, in turn, be questioned.
149 citations
TL;DR: The conflict theory proposes that imprinting is an intra-individual manifestation of classical parent-offspring conflict, and is unique in predicting that imprinted genes expressed from the paternally derived genome should be enhancers of pre- and post-natal growth, while those expression from the maternallyderived genome shouldBe growth suppressors.
96 citations
TL;DR: Contrary to the expectations of the conflict hypothesis, there is no evidence for antagonistic coevolution of imprinted genes mediated by changes in sequence.
Abstract: Genomically imprinted genes are those for which expression is dependent on the sex of the parent from which they are derived. Numerous theories have been proposed for the evolution of genomic imprinting; one theory is that it is an intra–individual manifestation of classical parent–offspring conflict. This theory is unique in predicting that an arms race may develop between maternally and paternally derived genes for the control of foetal growth demands. Such antagonistic coevolution may be mediated through changes in the structure of the proteins concerned. Comparable coevolution is the most likely explanation for the rapid changes seen in antigenic components of parasites and antigen recognition components of immune systems. We have examined the evolution of insulin–like growth factor ( Igf2 ) and its antagonistic receptor ( Igf2r ) and find that, in contrast to immune genes, at the sites of mutual binding they are highly conserved. In addition, we have analysed the rate of molecular evolution of seven imprinted genes (including Igf2 and Igf2r ), sequenced in both mouse and rat, and find that this is the same as that of non–imprinted receptors and significantly lower than that of immune genes (controlling for differences in mutation rate). Contrary to the expectations of the conflict hypothesis, we hence find no evidence for antagonistic coevolution of imprinted genes mediated by changes in sequence.
49 citations
TL;DR: A large number of invertebrate species that contain individuals whose offspring are almost all female can now be explained by the diverse actions of various ‘selfish’ elements residing in the cytoplasm of the individuals.
Abstract: Evolutionary theory predicts that most populations should consist of roughly as many males as females. Recently, a variety of populations have been described which show very different proportions of the two sexes, especially in invertebrate species that contain individuals whose offspring are almost all female. Some of these instances can now be explained by the diverse actions of various ‘selfish’ elements residing in the cytoplasm of the individuals, which are transmitted exclusively through the female line. These instances of curious sex ratios exemplify an important principle: the fitness of genes, rather than of individuals, is the primary currency of evolution.