Lecture Notes on Evolutionary Advantage of Sex | ECOL 320H, Study notes of Genetics

Download Lecture Notes on Evolutionary Advantage of Sex | ECOL 320H and more Study notes Genetics in PDF only on Docsity! Evolutionary Advantage of Sex AS ?S/A A S/A A S/A A S S/A A Ancestral eukaryote probably alternated asexual and sexual reproduction. If so, all strictly asexual organisms lost sexual reproduction. S = Sexual only A = Asexual only S/A = Sexual and asexual Possible locations of root Why? Many different models and theories: Hill-Robertson effect Muller’s ratchet Kondrashov’s hatchet Red Queen Etc, etc, etc ad ifinitum and ad nauseum Most can be included in one general statement: Natural selection works better with sex than without it. Simplistic model: AB AB AB AB detrimental mutations Ab aB AB AB Selection against b and a is balanced by selection for A and B. sex ab AB AB AB Without sex, asexuals tend to • lose advantageous mutations needed to adapt to different habitats (lower speciation rate) and adapt to changing environments (higher extinction rate) • fix detrimental mutations, leading to higher rate of extinction (Muller’s ratchet) Some puzzling exceptions: Animal mitochondrial genomes are effectively asexual, so why haven’t they (and we) gone extinct? Darwinulid ostracods, oribatid mites, and bdelloid rotifers have reproduced only by parthenogenesis for tens of millions of years and have undergone some speciation. Bdelloid rotifers show no accumulation of detrimental mutations; why not? Dehydration rejuvenates? Many groups of asexual eukaryotic microorganisms are ancient and have many species: • green alga “genus” Chlorella • all of the Excavates Having rare, furtive, or cryptic sex?