Population genetics and evolution of genomic imprinting

At a small number of mammalian loci, only one of the two copies of a gene is expressed. Just which copy is expressed depends on the sex of the parent from which that copy was inherited. Such genes are said to be imprinted. The functional haploidy implied by imprinting has a number of population genetic consequences. Moreover, since diploidy is widely believed to be advantageous, the evolution of this non-Mendelian form of expression requires an explanation. Here I examine some of the theoretical and mathematical models investigating these two aspects of imprinting. For instance, the dynamics and equilibrium properties of many models of natural selection at imprinted loci are formally equivalent to models without imprinting. And different approaches to modeling the problem of the evolution of imprinting reveal the weakness of several of the apparent predictions of various verbal hypotheses about why imprinting has evolved.