Although identical twins have identical DNA, they often harbor clear-cut differences: slight variations in appearance or stark distinctions in disease susceptibility, for example. Scientists have suggested that the interplay between nature and nurture could explain such differences, but the mechanism has been poorly understood.
A new study suggests that as identical twins go through life, environmental influences differently affect which genes are turned on and which are switched off.
Called epigenetic modification, such gene activation or silencing typically stems from two types of chemical groups that latch on to chromosomes as charms attach to a bracelet, says Manel Esteller of the Spanish National Cancer Centre in Madrid. Methyl groups that clip on to DNA tend to turn genes off. On the other hand, acetyl groups attaching to histones, the chemical core of chromosomes, usually turn genes on.