tailieunhanh - Báo cáo y học: " Genomic clues to an ancient asexual scandal"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Critical Care giúp cho các bạn có thêm kiến thức về ngành y học đề tài: Genomic clues to an ancient asexual scandal. | Minireview Genomic clues to an ancient asexual scandal William R Rice and Urban Friberg Address Department of Ecology Evolution and Marine Biology University of California Santa Barbara CA 93106 USA. Correspondence William R Rice. Email rice@ Published 28 December 2007 Genome Biology 2007 8 232 doi gb-2007-8-l2-232 The electronic version of this article is the complete one and can be found online at http 2007 8 12 232 2007 BioMed Central Ltd Abstract Despite abandoning meiosis the bdelloid rotifers have persisted for millions of years and given rise to hundreds of species. Several mechanisms - allelic variants with different functions high effective population size and resistance to radiation - may contribute to their success. Bdelloid rotifers are diploid aquatic microinvertebrates that live in fresh or brackish water especially in ephemeral habitats prone to periodic desiccation. They are the only well documented lineage that has eliminated meiosis yet has persisted for many millions of years more than 35 million years 1 and undergone an adaptive radiation - nearly 400 species in three families. Maynard Smith 2 referred to them as an evolutionary scandal because they are the exception to the usual pattern that asexual lineages die out before undergoing extensive speciation. The fact that asexuals are composed entirely of offspringproducing females gives them an intrinsic demographic advantage over sexual competitors whenever males do not help to produce offspring referred to as the two-fold cost of sex or the cost of producing males . Evolutionary theory predicts however that obligate asexuals have a long-term evolutionary disadvantage compared with sexuals owing to a more pronounced Hill-Robertson effect a reduction in the efficacy of natural selection that occurs because finite populations accumulate associations of linked genes haplotypes that interfere with selection 3 4 Figure 1 . The Hill-Robertson effect arises .