An adaptive hypothesis for the evolution of the Y chromosome.
Population geneticists remain unsure of the forces driving the evolution of Y chromosomes. Here we consider the possibility that the degeneration of the Y reflects its inability to evolve adaptively. Because the overwhelming majority of favorable mutations on a nonrecombining proto-Y suffer a zero probability of fixation, the fitness of the Y must lag far behind that of the recombining X. At some point, this disparity will grow so large that selection favors an increase in the expression of (fit) X-linked alleles and a decrease in the expression of (unfit) Y-linked alleles. Our calculations suggest that this process acts far more rapidly than hitchhiking-induced erosion of the Y and at least as rapidly as the fixation of deleterious alleles on the Y by background selection. Most important, this hypothesis can explain the evolution of Y chromosomes in taxa such as Drosophila that have very large population sizes.
Orr
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HA
Department of Biology, University of Rochester, Rochester, New York 14627, USA. urhep.pas.rochester.edu
Kim
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Y
D000220:Adaptation, Biological; D019143:Evolution, Molecular; D008432:Mathematical Computing; D008957:Models, Genetic; D012641:Selection, Genetic; D014998:Y Chromosome