Genomic imprinting as a coopted evolutionary character

Non-conflict theories for the evolution of genomic imprinting

Theories focused on kinship and the genetic conflict it induces are widely considered to be the primary explanations for the evolution of genomic imprinting. However, there have appeared many competing ideas that do not involve kinship/conflict. These ideas are often overlooked because kinship/conflict is entrenched in the literature, especially outside evolutionary biology. Here we provide a critical overview of these non-conflict theories, providing an accessible perspective into this literature. We suggest that some of these alternative hypotheses may, in fact, provide tenable explanations of the evolution of imprinting for at least some loci.

Host defenses to transposable elements and the evolution of genomic imprinting

Genomic imprinting is the differential expression of maternally and paternally inherited alleles of specific genes. Several organismic level hypotheses have been offered to explain the evolution of genomic imprinting. We argue that evolutionary explanations of the origin of imprinting that focus exclusively on the organismic level are incomplete. We propose that the complex molecular mechanisms that underlie genomic imprinting originally evolved as an adaptive response to the mutagenic potential of transposable elements (TEs). We also present a model of how these mechanisms may have been co-opted by natural selection to evolve molecular features characteristic of genomic imprinting.

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.