When two or more nonallelic gene pairs affect the same character in the same way, it is called

The correct answer is polygenic inheritance.

To understand this concept, let us break down the terms and the biological mechanism:
1. Nonallelic Gene Pairs: These are genes located at different loci (positions) on the same chromosome or on different chromosomes. They are not alleles of the same gene.
2. Affecting the Same Character: When multiple independent genes contribute to the determination of a single phenotypic trait (such as human skin color, height, or eye color), they work together to shape that characteristic.
3. Polygenic Inheritance: This term specifically describes a inheritance pattern where a single trait is controlled by two or more nonallelic genes. The effects of these genes are often additive, meaning each dominant allele contributes a unit of influence to the final phenotype, leading to continuous variation in the population.

Let us briefly review why the other options are incorrect:
- Pleiotropy: This is the opposite scenario, where a single gene influences multiple, seemingly unrelated phenotypic traits.
- Additive expressivity / Total penetrance: Penetrance refers to the proportion of individuals carrying a particular variation of a gene (allele) who also express an associated trait. Expressivity refers to the variations in a phenotype among individuals carrying a particular genotype. Neither of these terms describes multiple nonallelic genes controlling a single trait in the same way.