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? 

Verified step by step guidance

1. Step 1: Begin by analyzing the inheritance pattern observed in the F₁ generation. The F₁ hybrids exhibit intermediate eye size, which suggests incomplete dominance or additive genetic effects. This means that neither the cavefish nor the lakefish allele is completely dominant over the other.
2. Step 2: Examine the F₂ generation results. If the F₂ generation shows a range of eye sizes, including sizes similar to cavefish, lakefish, and intermediate sizes, this indicates that multiple genes may be involved in determining eye size. This is consistent with polygenic inheritance.
3. Step 3: Consider the backcross results (F₁×cavefish and F₁×lakefish). If the backcrosses produce offspring with eye sizes closer to the parent species (cavefish or lakefish), this suggests that the alleles from the parent species are influencing the trait in a predictable manner, further supporting the idea of additive genetic effects.
4. Step 4: Evaluate whether the inheritance pattern aligns with Mendelian ratios. If the F₂ generation does not follow simple Mendelian ratios (e.g., 3:1 or 1:2:1), this reinforces the hypothesis that eye size is controlled by multiple genes rather than a single gene.
5. Step 5: Conclude that the most feasible explanation for the inheritance of eye size is polygenic inheritance with additive effects, where multiple genes contribute to the trait, and the alleles from cavefish and lakefish interact to produce intermediate phenotypes in hybrids.

Key Concepts

Inheritance Patterns

Inheritance patterns refer to the ways in which traits are passed from parents to offspring. In genetics, these patterns can be classified as dominant, recessive, or co-dominant. Understanding these patterns is crucial for interpreting the results of genetic crosses, such as those involving F₁ and F₂ generations, as they help explain how traits like eye size can vary among hybrids and their progeny.

Hybridization

Hybridization occurs when two different species or varieties breed to produce offspring, known as hybrids. In the context of Wilkens's study, the F₁ hybrids exhibit intermediate eye sizes, suggesting that the traits for eye size from cavefish and lakefish may interact in a way that does not favor one parent over the other. This concept is essential for understanding the phenotypic outcomes observed in the F₁ and F₂ generations.

Quantitative Traits

Quantitative traits are characteristics that are influenced by multiple genes and can show a range of phenotypes, such as eye size in fish. These traits often follow a continuous distribution rather than discrete categories. In Wilkens's research, the variation in eye size among cavefish, lakefish, and their hybrids indicates that eye size is likely a quantitative trait, which complicates the inheritance patterns and necessitates a deeper analysis of genetic interactions.