mentalist, the theory of heredity as formulated by Gregor Mendel, i.e. a) the principle stating that during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent; law of segregation; b) the principle stating that the laws of chance govern which particular characteristics of the parental pairs will occur in each individual offspring; law of independent assortment; c) the principle stating that one factor in a pair of traits dominates the other in inheritance unless both factors in the pair are recessive; law of dominance.