Identical twins possess exactly the same set of genes. Yet as they grow older,
they may begin to display subtle differences. They may start to look different,
develop different diseases or slide into different persons. 1.______
Women who are identical twins may differ with their fertility or 2.______
the age at which they reach menopause. These discrepancies
usually attributed to ill-defined differences in environment. 3.______
But a whole new level of explanation has been opened up by a generic survey 4.______
showing that identical twins, because they grow older, differ increasingly in 5.______
what is known as their epigenome. The term refers to natural
chemical modifications that occur in a person’s genome shortly before 6.______
conception and that act on a gene as a gas pedal or a brake, marking it for higher or lower activity. 7.______
Identical twins have the same set of epigenetic mark on the genome 8.______
when they are born. But differences in the epigenome disappear 9.______
as the twins grow older and become greater the longer they live together, 10.______
say a team of researchers led by Dr. Manel Esteller of the Spanish National Cancer Center in Madrid.