In a line of cherry tomatoes, the average fruit weight is 16 g. A plant producing tomatoes with an average weight of 12 g is used in one self-fertilization cross to produce a line of smaller tomatoes, and a plant producing tomatoes of 24 g is used in a second cross to produce larger tomatoes. If narrow sense heritability (h²) for this trait is 0.80, what are the expected responses to selection (R) for fruit weight in the crosses?

Verified step by step guidance

1. Determine the formula for the response to selection (R). The response to selection is calculated using the equation: $R=h^2\cdot S$, where $h^2$ is the narrow sense heritability and $S$ is the selection differential.
2. Calculate the selection differential (S) for each cross. The selection differential is the difference between the mean phenotype of the selected parents and the mean phenotype of the original population. For the first cross, $S=\mathrm{12}-\mathrm{16}$. For the second cross, $S=\mathrm{24}-\mathrm{16}$.
3. Substitute the narrow sense heritability (h² = 0.80) into the formula for R. For each cross, the response to selection is calculated as: $R=h^2\cdot S$.
4. For the first cross, substitute the value of $S=\mathrm{12}-\mathrm{16}$ into the formula. This gives: $R=0.80\cdot (\mathrm{12}-\mathrm{16})$.
5. For the second cross, substitute the value of $S=\mathrm{24}-\mathrm{16}$ into the formula. This gives: $R=0.80\cdot (\mathrm{24}-\mathrm{16})$.

Key Concepts

Narrow Sense Heritability (h²)

Narrow sense heritability (h²) quantifies the proportion of phenotypic variance in a trait that can be attributed to additive genetic variance. It is crucial for predicting the response to selection, as it indicates how much of the trait's variation is heritable and 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.

Response to Selection (R)

Response to selection (R) is the expected change in the mean phenotype of a trait in a population after selection has occurred. It can be calculated using the formula R = h² × S, where S is the selection differential, representing the difference between the mean phenotype of the selected individuals and the overall population mean. Understanding R helps predict how traits will evolve under selective pressures.

Selection Differential (S)

The selection differential (S) measures the difference between the average phenotype of selected individuals and the average phenotype of the entire population before selection. It reflects the intensity of selection applied to a trait. In the context of the cherry tomatoes, calculating S for both crosses will allow for the determination of how much the average fruit weight is expected to change as a result of the selection process.