David The answer to your question is 'yes'. However, you are also correct in saying that genes are not the only determinant of how an organism develops.
Environment also has a role to play.
Identical twins are very similar but they are not completely identical. They think a bit differently, know different things and those that know them really well can generally tell them apart just by looking at them. This is the extent of the environment's role in our development. The rest is genes. Thanks for your question.