Gene experssion are influenced by enviroment. the best example is skin color in case of human for e.g if person with fair color or white complexion goes to africa or any part where sun exposure is more his or her color gets dark .the darking of skin is due to melanin production. see here person is same only difference is in enviromental condition due to which gene which are responsible for the production of melanin are produced.
I hope u understood it