Identical twins who have separate placentas are somewhat less similar than identical twins who share a placenta. This best illustrates the influence of on development.

prenatal environments

Explanation:

Depending on the number of fertilized eggs and when the zygote division occurs, there are different types of twins. For example, If the zygote is formed by the union of an ovule and a sperm that after fertilization is divided to create two embryos, they are born identical twins, these babies carry the same genetic information.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."