DO IMPRINTED GENES HAVE FEW AND SMALL INTRONS

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 strik ing but their interpretation is unclear. The loss of introns after a g ene becomes imprinted is not sufficient to explain why imprinted genes have fewer introns than average, because related unimprinted genes al so 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.