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 e ffect on patrilineal kin when paternally derived. However, the allele is no t subject to selection on its effects on patrilineal kin when maternally de rived nor on its effects on matrilineal kin when paternally derived. As a r esult, natural selection may favor alleles with effects that differ, depend ing on the allele's parental origin. At autosomal loci, this process is pre dicted to lead to the silencing of alleles when inherited from one or the o ther parent. At X-linked loci subject to random X inactivation, the process is predicted to lead to quantitative differences of expression between mat ernal and paternal alleles but not to complete silencing of one allele. The implications of this theory and some challenges to the theory are reviewed .