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 three possible genotypes that could account for F₂ plants that are 18 cm high and three that account for F₂ plants that are 33 cm high.

Key Concepts

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical or biochemical characteristics resulting from the genotype and environmental influences. In this context, the height of the plants is the phenotype, which can vary even among individuals with the same genotype due to factors like dominance, recessiveness, and environmental conditions.

Mendelian Inheritance

Mendelian inheritance describes the patterns of inheritance for traits controlled by single genes, as established by Gregor Mendel. In this scenario, the height of the plants likely follows Mendelian ratios, where dominant and recessive alleles interact to produce a range of phenotypes in the F₂ generation, leading to the observed variation in heights.

Polygenic Inheritance

Polygenic inheritance involves multiple genes contributing to a single trait, resulting in a continuous range of phenotypes. The variation in heights among the F₂ plants suggests that height is influenced by several genes, which can combine in different ways to produce intermediate phenotypes, such as the 18 cm and 33 cm heights mentioned in the question.