In 1988, Horst Wilkens investigated blind cavefish, comparing them with members of a sibling species with normal vision that are found in a lake [Wilkens, H. (1988). Evol. Biol. 25:271–367]. We will call them cavefish and lakefish. Wilkens found that cavefish eyes are about seven times smaller than lakefish eyes. F₁ hybrids have eyes of intermediate size. These data, as well as the F₁×F₁ cross and those from backcrosses (F₁×cavefish and F₁×lakefish), are depicted below. Examine Wilkens's results and respond to the following questions:

Based strictly on the F₁ and F₂ results of Wilkens's initial crosses, what possible explanation concerning the inheritance of eye size seems most feasible? 

Key Concepts

Inheritance Patterns

Inheritance patterns describe how traits are passed from parents to offspring through genes. In this context, understanding whether eye size is influenced by dominant or recessive alleles is crucial. The F₁ hybrids exhibiting intermediate eye size suggest incomplete dominance, where neither allele is completely dominant, leading to a blending of traits in the offspring.

Hybridization and F₁ Generation

Hybridization occurs when two different species or varieties breed, producing hybrids. The F₁ generation refers to the first filial generation of offspring from a cross. In this case, the F₁ hybrids of cavefish and lakefish show intermediate eye sizes, indicating that the traits for eye size from both parent species contribute to the phenotype of the hybrids.

Backcrossing

Backcrossing is a breeding method where hybrids are crossed with one of their parent species. This technique helps to analyze the inheritance of specific traits, such as eye size in this study. By examining the results of backcrosses (F₁×cavefish and F₁×lakefish), researchers can determine the genetic contributions of each parent and further clarify the inheritance pattern of eye size.