The kinship theory of genomic imprinting

The inclusive fitness effect attributable to an allele can be divided into an effect on matrilineal kin when the allele is maternally derived and an effect on patrilineal kin when paternally derived. However, the allele is not subject to selection on its effects on patrilineal kin when maternally derived nor on its effects on matrilineal kin when paternally derived. As a result, natural selection may favor alleles with effects that differ, depending on the allele's parental origin. At autosomal loci, this process is predicted to lead to the silencing of alleles when inherited from one or the other parent. At X-linked loci subject to random X inactivation, the process is predicted to lead to quantitative differences of expression between maternal and paternal alleles but not to complete silencing of one allele. The implications of this theory and some challenges to the theory are reviewed.