Monoalleleic transcription of the insulin-like growth factor-II gene (Igf2) in chick embryos.

A polymorphism in the igf2 gene of chickens was identified using NlaIII (GenBank accession number AF218827). In some embryos, the igf2 alleles were expressed monoallelically from either maternal or paternal alleles. These data demonstrate that genomic imprinting is not confined to mammalian vertebrates and suggest that genomic imprinting evolved at an early stage of vertebrate evolution. The observations that the igf2 gene is imprinted in a minority of embryos suggest that the imprinting in birds is unrelated to embryonic growth. Genome imprinting may provide opportunities for evolution of genes in a nonexpressed state. In poultry breeding, the presence of imprinted genes may make a major contribution to unequal performance in reciprocal matings between commercial lines.