Gina and tina are identical twins. gina has had a series of traumas and has been diagnosed with schizophrenia. tina is demonstrating no symptoms of schizophrenia. because schizophrenia tends to run in families, the difference between the twins can be explained through
a) the stress of childbirth.
b) cultural influences.
c) the medical model
d) epigenetics.

d) epigenetics.    

Explanation:

Epigenetics: In psychology, epigenetics gives a framework for apprehension about how the genes are influenced by the environment and experiences to produce individual differences in cognition, personality, mental health, and behavior. Epigenetic changes the physical composition of the DNA.

Example: Histone modification.

Epigenetics has a very strong influence or effect on the development of a human being or any organism and can even alter the expression of the individual traits.

using the scientific method.

the branch of biology that deals with the normal functions of living organisms and their parts.

the way in which a living organism or bodily part functions.