11 Evolution of sex - BIO 370 Kirkpatrick Hall Fall 2004 p...

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BIO 370 Kirkpatrick & Hall, Fall 2004 p. 1 11. Evolution of sex The large majority of metazoans reproduce sexually A small number are parthenogenetic (asexual): females make eggs that are genetic copies of themselves (other than rare new mutations) Asexual species are usually found on the tips of evolutionary trees Their close evolutionary relatives are sexual species This tells us that most asexual species do not persist long in time The one large exception: bdelloid rotifers About 130 species that have evolved without sex for about 40 million years It is mysterious why sexual reproduction is common: we can think of several reasons why it should be rare 1. The two-fold cost of meiosis All else equal, asexual species should reproduce at twice the rate of a sexual species in which half the individuals are male Another way to look at it: a mutation in a sexual species which causes females to produce parthenogenetic daughters has a 100% fitness advantage ( s = 1)
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