Effect of environment on genes is called –
Eugenics 

Science which aims to improve the genetic endowment of human population.
That is improving the quality of the human species or a human population by genetic manipulation.
Eugenic may be :


Negative →        Discouraging reproduction by persons having genetic defect or presumed to have inheritable undesirable traits this includes abortions, sterilization & other methods family planning.
Positive Eugenics → Encouraging reproduction presumed to have inheritable desirable trait. For example, in vitro-fertilization, cloning, egg transplantation etc.

Euthenics 

Euthenics deal with human improvement through altering the external environment (environmental manipulation).
It includes education, prevention and removal of contagious disease and parasites, education regarding home economics, sanitation and housing.
Positive Eugenics
Negative Eugenics
Euthenics
Enthenics