Mitochondria, mating types and sexes.

Zena Hadjivasiliou
(University College London)

12/10/9, 13:30 - 14:30 at the 2nd meeting room (5th floor of building 3 of the Faculty of Sciences)

The existence of binary mating systems in the vast majority of sexual organisms has long been an evolutionary puzzle. Why mating partners need to be of different type or sex is unclear. A possible explanation relates to mitochondrial inheritance. Uniparental inheritance (UPI) of mitochondria is widely spread in many taxa. Several studies have proposed that two sexes evolved as a respond to the need for UPI so that one sex passes on its mitochondria whereas the other does not. In this work we re-assess these postulations by developing a novel mathematical model which explicitly considers mitochondrial evolution and the parallel evolution of genes imposing uniparental inheritance. Our results suggest that UPI of mitochondria would spread in a biparental population but never to fixation without pre-existing mating types. This is because the fitness benefits ‘leak’ through the population as a result of successive uniparental and biparental matings. Only when binary mating types already exist can uniparental mutants spread to fixation. We conclude that the requirement for UPI probably did not drive the evolution of two mating types, but is readily fixed afterwards, giving rise to the patterns actually seen in protists.

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