An inbred strain of plants has a mean height of 24 cm. A second strain of the same species from a different geographic region also has a mean height of 24 cm. When plants from the two strains are crossed together, the F₁ plants are the same height as the parent plants. However, the F₂ generation shows a wide range of heights; the majority are like the P₁ and F₁ plants, but approximately 4 of 1000 are only 12 cm high and about 4 of 1000 are 36 cm high.

How much does each gene contribute to plant height?

Key Concepts

Heritability

Heritability refers to the proportion of variation in a trait, such as plant height, that can be attributed to genetic differences among individuals in a population. It is crucial for understanding how much of the observed height variation in the F₂ generation is due to genetic factors versus environmental influences. High heritability suggests that genetics play a significant role in determining the trait.

Quantitative Trait Loci (QTL)

Quantitative Trait Loci are specific regions of the genome that are associated with the variation in quantitative traits, like height. In this scenario, the wide range of heights in the F₂ generation indicates that multiple genes likely influence plant height, and QTL mapping can help identify these genes and their contributions to the trait's expression.

Dominance and Epistasis

Dominance refers to the relationship between alleles where one allele can mask the expression of another. Epistasis involves interactions between different genes, where the effect of one gene is modified by one or several other genes. Understanding these concepts is essential to explain why the F₁ generation resembles the parent strains, while the F₂ generation exhibits a broader range of heights due to the complex interplay of multiple genes.