The correct answer is blood type.
The blood type of the individual in determined by the genes they inherit from their parents, it has no environmental influence.
The skin color is determined by the genes, but the main reason behind the presence of the skin color is melanin pigments. The melanin pigments present in the skin can increase to a significant level, if the exposure to sun is more. So, it is not alone determined by the genes.
The athletic ability and the muscle mass are acquired by exercising and physical training. It has a little genetic influence, it is mainly determined by the amount of exercise a person do.
