Height in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci R, S, T, and U and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height.

Can two individuals of moderate height produce offspring that are much taller or shorter than either parent? If so, how?

Key Concepts

Additive and Partially Additive Alleles

Additive alleles contribute a fixed amount to a trait, in this case, height, with each allele adding two units. Partially additive alleles contribute less, specifically one unit. The combination of these alleles from both parents can lead to a range of phenotypic expressions in offspring, allowing for variability in traits like height.

Polygenic Inheritance

Height is a polygenic trait, meaning it is influenced by multiple genes (loci). In this scenario, four loci (R, S, T, U) are involved, and the cumulative effect of the alleles at these loci determines the overall height of an individual. This complexity allows for a wide range of possible heights in offspring, even if both parents are of moderate height.

Phenotypic Variation

Phenotypic variation refers to the observable differences in traits among individuals, which can arise from genetic differences and the interaction of multiple alleles. In the context of height, two moderate-height parents can produce offspring that are significantly taller or shorter due to the various combinations of additive and partially additive alleles inherited from both parents, leading to a diverse range of heights.