No abstract

A subset of genes in mammals, known as imprinted genes, show a conditional expression strategy in which transcription depends on an allele's parental origin. Several explanations have been advanced to explain this phenomenon and these, with varying levels of success, predict the functions of imprinted genes. After outlining these explanations, we summarize what is known about human genetic disorders involving abnormal expression of imprinted genes and ask what this can tell us about the evolution of imprinting.