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: Wilkens examined about 1000 F₂ progeny and estimated that 6–7 genes are involved in determining eye size. Is the sample size adequate to justify this conclusion? Propose an experimental protocol to test the hypothesis.

Key Concepts

Genetic Inheritance

Genetic inheritance refers to the process by which traits and characteristics are passed from parents to offspring through genes. In the context of the cavefish and lakefish, understanding how eye size is inherited is crucial, as it involves multiple genes that contribute to phenotypic variation. The study of F₁ hybrids and their F₂ progeny helps illustrate how traits can segregate and combine in subsequent generations.

Quantitative Trait Loci (QTL)

Quantitative Trait Loci (QTL) are regions of the genome that are associated with the variation in a quantitative trait, such as eye size in fish. The identification of 6-7 genes influencing eye size suggests that this trait is polygenic, meaning it is controlled by multiple genes, each contributing to the overall phenotype. Understanding QTL is essential for designing experiments to map these genes and their effects on eye size.

Sample Size and Statistical Power

Sample size and statistical power are critical in experimental design, as they determine the reliability of the conclusions drawn from data. A sample size of about 1000 F₂ progeny is generally considered adequate for detecting genetic effects, but the power to detect specific gene interactions or effects may vary. Evaluating whether the sample size justifies Wilkens's conclusion about the number of genes involved requires understanding statistical methods and the expected effect sizes.