Abstract

A gene is described as imprinted if its pattern of expression depends on whether it passed the previous generation in a male or female germ line. A recent paper(1) reports that imprinted genes have fewer and smaller introns than a control set of genes. The differences are striking but their interpretation is unclear. The loss of introns after a gene becomes imprinted is not sufficient to explain why imprinted genes have fewer introns than average, because related unimprinted genes also have few introns. Similarly, small introns appear to be a property of chromosomal region rather than of imprinting status itself, because neighboring unimprinted genes also have small introns.