Suppose the length of maize ears has narrow sense heritability (h²) of 0.70. A population produces ears that have an average length of 28 cm, and from this population a breeder selects a plant producing 34-cm ears to cross by self-fertilization. Predict the selection differential (S) and the response to selection (R) for this cross.

Verified step by step guidance

1. Understand the key terms: Narrow sense heritability (h²) is the proportion of phenotypic variance that is due to additive genetic variance. The selection differential (S) is the difference between the mean phenotype of the selected parents and the mean phenotype of the original population. The response to selection (R) is the change in the mean phenotype of the offspring population due to selection, calculated as R = h² × S.
2. Calculate the selection differential (S): Subtract the mean phenotype of the original population (28 cm) from the phenotype of the selected parent (34 cm). This gives S = 34 - 28.
3. Recall the formula for the response to selection (R): Use the equation R = h² × S, where h² is the narrow sense heritability (0.70) and S is the selection differential calculated in the previous step.
4. Substitute the values into the formula: Replace h² with 0.70 and S with the value obtained in step 2. This will give you the predicted response to selection (R).
5. Interpret the results: The response to selection (R) represents the expected increase in the mean ear length of the offspring population compared to the original population. Add this value to the original population mean (28 cm) to predict the new mean ear length in the offspring population.

Key Concepts

Narrow Sense Heritability (h²)

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 it indicates how much of the trait's variation can be passed on to the next generation. A higher h² value suggests that selection will be more effective in altering the trait in future generations.

Selection Differential (S)

The selection differential (S) is the difference between the mean phenotype of the selected individuals and the mean phenotype of the entire population. It measures the intensity of selection and is a key factor in determining how much the average trait value will change in the next generation. A larger S indicates stronger selection pressure, leading to a greater potential change in the trait.

Response to Selection (R)

Response to selection (R) is the expected change in the mean phenotype of a trait in the next generation as a result of selection. It can be calculated using the formula R = h² × S, where h² is the narrow sense heritability and S is the selection differential. Understanding R helps breeders predict how effective their selection strategies will be in achieving desired trait improvements.