A hypothetical study investigated the vitamin A content and the cholesterol content of eggs from a large population of chickens. The following variances (V) were calculated.

Which trait, if either, is likely to respond to selection?

Verified step by step guidance

1. Step 1: Understand the variances given in the table. \(V_P\) is the phenotypic variance, which is the total observed variance in the trait. \(V_E\) is the environmental variance, representing variation due to environmental factors. \(V_A\) is the additive genetic variance, which is the portion of genetic variance that contributes to resemblance between parents and offspring. \(V_D\) is the dominance genetic variance, which arises from interactions between alleles at the same locus.
2. Step 2: Recall that the response to selection depends primarily on the additive genetic variance (\(V_A\)) because only additive effects are reliably passed from parents to offspring and thus contribute to heritability.
3. Step 3: Calculate the narrow-sense heritability (\(h^2\)) for each trait using the formula: \[h^2 = \frac{V_A}{V_P}\] This ratio tells us the proportion of phenotypic variance that is due to additive genetic variance.
4. Step 4: Compare the \(h^2\) values for Vitamin A and Cholesterol. The trait with the higher \(h^2\) is more likely to respond to selection because it has a greater proportion of additive genetic variance relative to total phenotypic variance.
5. Step 5: Conclude which trait is likely to respond to selection based on the calculated heritabilities, keeping in mind that traits with low additive genetic variance or low heritability will respond less effectively to selection.

Key Concepts

Phenotypic Variance (V_P)

Phenotypic variance represents the total observed variation in a trait within a population. It includes genetic variance (both additive and dominance) and environmental variance. Understanding V_P is essential to partition the sources of variation affecting the trait.

Additive Genetic Variance (V_A)

Additive genetic variance is the portion of genetic variance attributed to the additive effects of alleles. It is crucial for predicting response to selection because only additive effects are reliably passed from parents to offspring, influencing trait heritability.

Heritability and Response to Selection

Heritability in the narrow sense is the ratio of additive genetic variance to phenotypic variance (h² = V_A / V_P). Traits with higher heritability are more likely to respond to selection because additive genetic effects drive evolutionary change.