Q: I am 6 months pregnant with twins. There is a common notion among people that it’s better to have twins of the same sex than different sex twins. Could you please tell me is it really better to have same sex twins rather than different sex?

A:Both genetics and environment influence our mental development. Most twin studies state the influence of genetic factors for the cognitive development and intelligence of twins, but not for their differences. Twins of different sex are most likely to be dizygotic and have very little chances of having exactly the same chromosomal or genetic profile. In other words, they are simply brothers and sisters who were born at around the same time. As for monozygotic twins, who are genetically identical, they become less alike as they grow older because of lifestyle choices and external influences. Even when they have the exact DNA, epigenetic modifications (switching of some genes under differing environmental influences) do occur, as they become older giving characteristic differences.