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Lecture 8

BIOL 2400 Lecture 8: Origin of Sex Class Notes

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BIOL 2400
Teresa Crease

BIOL*2400 Dr. Crease Winter 2017 Origin of Sex Lecture 8 Origin of Sexual Reproduction Evolutionary fitness is function of number of offspring produced o Reproduction may be sexual or asexual Asexual reproduction involves mitotic cell division and results in offspring that are genetically identical to parent o Very common in some animal phyla and plants capable of vegetative reproduction Expansion of colonies in sessile organisms is accomplished by asexual reproduction Sex or amphimixis refers to recombination of genetic material from more than one individual Sexual reproduction involves meiosis in which diploid cells become haploid and fuse with other haploid cells Sex can be decoupled from reproduction fusion of nuclei and subsequent meiosis of resulting zygote may create genetically recombinant cells without increasing total number of cells Parthenogenetic modes of reproduction have evolved sexually reproducing species in animal phyla and plants o has evolved in most major animal groups except birds and mammals o development of egg without fertilization derived from meiotic reproduction o many cytological mechanisms, some of which are not genetically equivalent to asexual reproduction Apomictic parthenogenesis: (meiosis 1 is suppressed) is equivalent to asexual reproduction because females produce offspring that are genetically identical to themselves, barring mutation Automixis refers to mechanisms in which 2 meiotic products from same parent fuse to form diploid zygote o in absence of recombination between homologues, leads to homozygosity 2fold genetic cost occurs because parents only pass half of their genes to each offspring 2fold ecological cost occurs because females must find males with which to mate before they can reproduce o does not apply to isogamous organisms Assumptions underlying 2fold costs of sex: o Females reproductive mode does not affect number of offspring she can make o Females reproductive mode does not affect probability of offspring survival o Recombination during mixis disrupts genotypes that have successfully survived and reproduced
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