Which parental gene gets the upper hand?

Things used to be relatively straightforward when it came to parental influences on gene action. Mom and Dad passed on one copy (or allele) of each autosomal gene to their progeny and overall, the expression and function of genes inherited by the offspring were indifferent to which parent they came from. When imprinted genes were discovered, this simple picture changed. That is because chemical modifications of DNA that occur early during development of the female and male germ line (the cells that form the egg and sperm) epigenetically mark imprinted genes for differential expression, depending on whether the gene is of maternal or paternal origin (1). In some cases, such imprinting suppresses expression from the maternal allele, leading to sole (or predominate) expression of the paternal copy of the gene. For other imprinted genes, the opposite is true and expression is solely or predominately from the maternal allele. On pages 643 and 682 of this issue, Gregg et al. (2, 3) provide new findings that influence current thinking about the scale and complexity of genomic imprinting and place parental influences on gene expression as a major player in the epigenetic regulation of brain function