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.

Indicate one possible set of genotypes for the original P₁ parents and the F₁ plants that could account for these results.

Key Concepts

Inbreeding and Genetic Variation

Inbreeding refers to the mating of closely related individuals, which can lead to a reduction in genetic variation. In the context of the question, the inbred strains of plants have a limited genetic pool, resulting in a consistent mean height. However, crossing these strains can introduce new combinations of alleles, leading to a wider range of phenotypes in the F₂ generation.

Mendelian Inheritance

Mendelian inheritance describes how traits are passed from parents to offspring through discrete units called alleles. In this scenario, the F₁ generation exhibits a phenotype similar to the parents, indicating dominance. The F₂ generation's varied heights suggest that multiple alleles are involved, and the observed ratios can be explained by Mendel's laws of segregation and independent assortment.

Phenotypic Ratios and Polygenic Traits

Phenotypic ratios refer to the relative frequencies of different phenotypes in a population. The wide range of heights in the F₂ generation suggests that plant height is a polygenic trait, influenced by multiple genes. The presence of extreme heights (12 cm and 36 cm) among the majority indicates that these traits may result from the additive effects of several alleles, leading to a continuous distribution of phenotypes.