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 on the results of the F₁ backcross with lakefish, is your explanation supported? Explain.

Verified step by step guidance

1. Step 1: Understand the genetic basis of the trait being studied. In this case, the size of the eyes in cavefish and lakefish is the trait of interest. The intermediate eye size in F₁ hybrids suggests incomplete dominance or additive genetic effects.
2. Step 2: Analyze the results of the F₁ backcross with lakefish. A backcross involves crossing an F₁ hybrid with one of the parental types (in this case, lakefish). This helps determine the inheritance pattern of the trait by observing the distribution of eye sizes in the offspring.
3. Step 3: Consider the expected phenotypic ratios. If the trait is controlled by a single gene with incomplete dominance, the offspring from the backcross should display a mix of phenotypes, including intermediate eye sizes and eye sizes closer to the lakefish parent.
4. Step 4: Compare the observed results with the expected ratios. If the observed phenotypes align with the expected ratios for incomplete dominance or additive effects, this supports the explanation that the trait is influenced by genetic factors with intermediate expression.
5. Step 5: Evaluate whether the data from the backcross supports the hypothesis. If the offspring show a range of eye sizes consistent with the genetic model proposed (e.g., intermediate dominance or additive effects), then the explanation is supported. If the results deviate significantly, alternative genetic mechanisms may need to be considered.

Key Concepts

Hybrid Vigor and Intermediate Traits

Hybrid vigor, or heterosis, refers to the phenomenon where hybrid offspring exhibit improved or enhanced biological qualities compared to their parents. In the context of the cavefish and lakefish, the F₁ hybrids show intermediate eye size, suggesting that the traits for eye size are influenced by multiple alleles from both parent species, leading to a phenotype that is a blend of both.

Backcrossing in Genetics

Backcrossing is a breeding method where hybrid offspring are crossed back with one of the parent species. This technique helps to analyze the inheritance of specific traits, such as eye size in this case. By examining the results of the F₁ backcross with lakefish, researchers can determine whether the traits are dominant, recessive, or influenced by multiple genes.

Quantitative Trait Loci (QTL)

Quantitative Trait Loci (QTL) are regions of the genome that are associated with specific quantitative traits, such as eye size. The study of QTL helps in understanding the genetic basis of traits that vary continuously in a population. In this scenario, identifying QTL related to eye size can provide insights into the genetic mechanisms underlying the differences observed between cavefish and lakefish.