Mutation x x mutation free chromosome x x double

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Unformatted text preview: will reproduce itself •  a new mutant that can asexually reproduce by cloning has a twofold advantage in reproduc*on –  assuming no male contribu*on to offspring –  only produces daughters –  should replace the sexual genotype (unless there are costs) hkp://www.indiana.edu/~curtweb/Research/cost%20of%20males.html so why are there so many sexual species? •  sexuality has been independently lost in many different lineages •  these tend to be evolu*onarily short lived –  recent origin •  some eukaryo*c groups – few or no recombinants found –  e.g. Bdelloid ro*fers –  e.g. Candida fungus hkp://en.wikipedia.org/wiki/Parthenogenesis so why are there so many sexual species? •  widely held view –  advantages of sex outweigh the disadvantages Popula*on thinking: recombina*on Population without recombination (ASEXUAL) Population with recombination (SEXUAL) X X X X X X X X Mutations occur and accumulate (reversal of individual mutations is very very very rare) Popula*on thinking: recombina*on ecombina*on Population without recombination (ASEXUAL) Population with recombination (SEXUAL) X X X X Selection gets rid of some or most How recombination helps a population eliminate deleterious mutation X X Mutation-free chromosome X X Double mutant chromosome The mutation free chromosome does great in the population The double mutant chromosome is quickly eliminated from the population THE ASEXUAL POPULATION CANNOT DO THIS Popula*on Popula*on thinking: recombina*on ecombina*on Population without recombination (ASEXUAL) Population with recombination (SEXUAL) X X X X X X X X X X X X OVER TIME, RECOMBINATION HELPS SEXUAL POPULATION KEEP THE NUMBER OF MUTATIONS AT A LOW NUMBER (EQUILIBRIUM BETWEEN SELECTION AND MUTATION) X Popula*on Popula*on thinking: recombina*on ecombina*on Population without recombination (ASEXUAL) Population with recombination (SEXUAL) X X X X X X X X X X X X X X X X X X X X X X X X X X X BUT THE POPULATION WITHOUT RECOMBINATION CONTINUES TO ACCUMULATE DELETERIOUS MUTATIONS X Popula*on Popula*on thinking: recombina*on ecombina*on Population without recombination (ASEXUAL) Population with recombination (SEXUAL) XX XX X X XX X X X X X X XX X X X X X X X X XX X X X XX XX X X X...
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This document was uploaded on 02/27/2014.

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