Cattle breeders would like to improve the protein content and butterfat content of milk produced by a herd of cows. Narrow sense heritability values are 0.60 for protein content and 0.80 for butterfat content. The average percentages of these traits in the herd and the percentages of the traits in cows selected for breeding are as follows. Trait Herd Average Selected Cows Protein content 20.2% 22.7% Butterfat content  6.5%  7.4% Which trait is likely to be the most responsive to artificial selection applied by the cattle breeders through selection of cows for mating?

Verified step by step guidance

1. Step 1: Understand the concept of narrow sense heritability (h²). Narrow sense heritability measures the proportion of phenotypic variance that is due to additive genetic variance. Traits with higher h² values are more responsive to selection because a larger proportion of the variation is heritable.
2. Step 2: Recall the breeder's equation: R = h² × S, where R is the response to selection, h² is the narrow sense heritability, and S is the selection differential. The selection differential (S) is calculated as the difference between the mean trait value of selected individuals and the mean trait value of the population.
3. Step 3: Calculate the selection differential (S) for each trait. For protein content, S = 22.7% - 20.2%. For butterfat content, S = 7.4% - 6.5%. Use these differences to determine the selection differential for each trait.
4. Step 4: Multiply the narrow sense heritability (h²) by the selection differential (S) for each trait to calculate the response to selection (R). For protein content, R = 0.60 × S. For butterfat content, R = 0.80 × S. This step will show which trait has a higher response to selection.
5. Step 5: Compare the calculated R values for protein content and butterfat content. The trait with the higher R value will be the most responsive to artificial selection applied by the cattle breeders.

Key Concepts

Narrow Sense Heritability

Narrow sense heritability (h²) quantifies the proportion of phenotypic variance in a trait that is attributable to additive genetic variance. It is crucial for predicting the response to selection, as higher h² values indicate that a trait is more likely to respond positively to selective breeding. In this case, the heritability values of 0.60 for protein and 0.80 for butterfat suggest that butterfat content has a greater potential for improvement through selection.

Response to Selection

Response to selection refers to the change in the average phenotype of a trait in a population following selective breeding. It is influenced by the heritability of the trait and the selection differential, which is the difference between the average trait value of selected individuals and the overall population. A higher response to selection is expected for traits with higher heritability and greater selection differentials, making it essential for breeders to evaluate these factors.

Selection Differential

The selection differential is the difference between the mean phenotype of selected individuals and the mean phenotype of the entire population. It reflects the intensity of selection applied by breeders. In this scenario, the selection differentials for protein and butterfat content can be calculated, and a larger differential indicates a stronger selection pressure, which, combined with heritability, helps predict which trait will respond better to artificial selection.