What is the term for two or more sets of alleles affect the same trait? Select one:
a. codominant
b. a double-trait cross
c. polygenic inheritance
d. polygenic dominance
e. a single-trait cross
The correct answer and explanation is:
The correct answer is: c. polygenic inheritance
Explanation:
Polygenic inheritance refers to a pattern of inheritance where two or more sets of alleles (or genes) affect the expression of a single trait. In this type of inheritance, the trait is controlled by multiple genes, each contributing to the overall phenotype. These genes may have additive effects, meaning the combined action of each allele leads to a continuous distribution of the trait’s phenotype. Examples of traits influenced by polygenic inheritance include skin color, height, and eye color in humans.
Unlike Mendelian traits, which are typically governed by a single gene with dominant and recessive alleles, polygenic traits do not follow simple dominant-recessive patterns. Instead, the phenotype results from the interaction of multiple alleles across different genes. These alleles may also show incomplete dominance or co-dominance, but the trait’s overall expression is the result of the cumulative effect of these genes.
For example, human skin color is controlled by several genes, each contributing a small amount to the total pigment in the skin. Individuals with more dark-pigment alleles will have darker skin, while those with more light-pigment alleles will have lighter skin. The variation in skin color across populations is a result of polygenic inheritance.
Polygenic inheritance leads to a wide range of phenotypic outcomes, often resulting in a continuous spectrum rather than discrete categories. This is why traits influenced by multiple genes often exhibit a bell-shaped curve when plotted on a graph.
Other options like codominance, a double-trait cross, and polygenic dominance do not accurately describe this form of inheritance, as they either refer to interactions between specific alleles or the study of two traits simultaneously, rather than the cumulative effects of multiple alleles influencing a single trait.