Genetic conflict in early development: parental imprinting in normal and abnormal growth.

Parental (genomic) imprinting is the process by which the differential expression of maternal and paternal alleles at certain genetic loci in mammalian embryos occurs. Such loci are implicated in the control of fetal, placental and neonatal growth, and, more generally, in diverse aspects of fetal nutrient acquisition and maternal-fetal interactions. Not surprisingly, the aberrant expression of imprinted genes is implicated in a range of embryonic and fetal abnormalities. We outline how an evolutionary theory, based on classic parent-offspring conflict theory, relates to certain fetal growth abnormalities. In particular, we suggest that growth abnormalities resulting from the manipulation of preimplantation mammalian embryos in vitro (for example large calf syndrome) may reflect the occurrence of genetic conflict over the fetal growth programme in the early preimplantation period.