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 gcne 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.