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Identical twins have the same DNA base sequence. As twins get older they often become more different from each other, for example one twin may develop a disease that the other does not. Scientists measured the total amount of DNA methylation in pairs of identical twins of different ages.
Analyse the relationship between the age of the twins and the difference in DNA methylation between them.
The twins have the same DNA base sequence. Explain how these data support the idea that the environment affects gene expression.
Suggest one reason why the scientists used pairs of identical twins rather than pairs of unrelated people.