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.

What mode of inheritance is occurring here?

Key Concepts

Inbreeding and Genetic Variation

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

Mendelian Inheritance

Mendelian inheritance describes the patterns of inheritance first outlined by Gregor Mendel, particularly the principles of segregation and independent assortment. In this scenario, the F₁ generation shows a uniform phenotype, indicating that the traits are likely controlled by a few alleles. The F₂ generation's variation suggests that multiple alleles are involved, leading to a range of phenotypes due to the recombination of alleles.

Polygenic Inheritance

Polygenic inheritance occurs when multiple genes influence a single trait, resulting in a continuous range of phenotypes. The wide range of heights observed in the F₂ generation, including the extremes of 12 cm and 36 cm, suggests that height is a polygenic trait. This means that several genes contribute to the final phenotype, leading to the observed variation in plant heights.