When one gene affects more than one phenotype, the phenomenon is called ___(A)___. When more than two genes affect one phenotype, the phenomenon is called __(B)__. Identify (A) and (B).

The correct option is B (A) - pleiotropism, (B) - polygenic inheritance
Pleiotropism refers to the effect of one gene on more than one character. So, (A) is pleiotropy.
Polygenic inheritance refers to the condition in which one character is controlled by multiple genes and each of them contributes some amount to the overall phenotype. In this case, the cumulative effect of these genes (polygenes) control the expression of the resultant phenotype. So, (B) matches with polygenic inheritance.
The phenomenon in which a gene has more than two alleles responsible for a phenotype is called multiple allelism. Those alleles are called multiple alleles. However, only two of them give the combination in a diploid individual.