<P> In insects, imprinting affects entire chromosomes . In some insects the entire paternal genome is silenced in male offspring, and thus is involved in sex determination . The imprinting produces effects similar to the mechanisms in other insects that eliminate paternally inherited chromosomes in male offspring, including arrhenotoky . </P> <P> In placental species, parent - offspring conflict can result in the evolution of strategies, such as genomic imprinting, for embryos to subvert maternal nutrient provisioning . Despite several attempts to find it, genomic imprinting has not been found in the platypus, reptiles, birds or fish . The absence of genomic imprinting in a placental reptile, the southern grass skink, is interesting as genomic imprinting was thought to be associated with the evolution of viviparity and placental nutrient transport . </P> <P> Studies in domestic livestock, such as dairy and beef cattle, have implicated imprinted genes (e.g. IGF2) in a range of economic traits, including dairy performance in Holstein - Friesian cattle . </P> <P> A similar imprinting phenomenon has also been described in flowering plants (angiosperms). During fertilisation of the egg cell, a second, separate fertilization event gives rise to the endosperm, an extraembryonic structure that nourishes the embryo in a manner analogous to the mammalian placenta . Unlike the embryo, the endosperm is often formed from the fusion of two maternal cells with a male gamete . This results in a triploid genome . The 2: 1 ratio of maternal to paternal genomes appears to be critical for seed development . Some genes are found to be expressed from both maternal genomes while others are expressed exclusively from the lone paternal copy . It has been suggested that these imprinted genes are responsible for the triploid block effect in flowering plants that prevents hybridization between diploids and autotetraploids . </P>

Different phenotype depending on parental origin of gene