In mammals and birds, females are born with all the oocytes required for future ovulations. These oocytes are not haploid: they are arrested at the Prophase I of meiosis when they have two sister chromatids of each chromosome (i.e. the eggs are at the 4C stage). Under the assumption that the low number of ovulated eggs in these species have been selected to be of high quality, I propose three explanations for these two observations: (I) producing the eggs before birth may decrease the variance in mutations and genetic damage, thereby reducing risk; (II) arresting the oocytes at a 4C stage may allow sister-strand recombination to repair genetic damage; (III) arresting the oocytes at the 4C stage may mitigate intergametic conflict, hence potential selection of the oocytes for ovulation will not involve conflict. Predictions from the Mutational, Repair, and Conflict Hypotheses are critically evaluated in the light of unpublished data, evolutionary theory, and computer simulations.
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