In one population of tomato plants, the mean fruit weight is 60g and the h^2 =0.

Question

In one population of tomato plants, the mean fruit weight is 60g and the h^2 =0.3. In a second population of tomato plants, the mean fruit weight is also 60g but h^2 =0.5. Predict the mean fruit weight among the progeny of tomato plants whose fruit weighta verages 80g in each population seperately. Why does the prediction differ between the two populations? The correct answer is: In population 1, 66g. In population 2, 70g. Population 2 shows a stronger response to selection because a larger fraction of the phenotypic variation in population 2 is comprised of additive genetic variation (h^2 = 0.5 vs. 0.3) and this predicts the response to selection. If someone could explain this step by step I would greatly appreciate it!

Explanation / Answer

The relationship between h2 (heritability) and the response to selection, is given by: R = h2S,

Where, R be the response to selection

&, S is the selection coefficient, given by the difference between the unselected population mean (60g or 66g; mean fruit weight of the entire population 1 or 2), and the mean of the selected parents (80g)

Here, for the first case, S = (80- 60) g = 20g

R = h2S = 0.3 X 20 = 6

The mean fruit weight of the population 1 after one generation of selection is therefore predicted to be: New mean = Unselected mean + predicted response = 60g + 6g = 66g

For the second case, S= (80- 60) g = 20g

R = h2S = 0.5 X 20 = 10

The mean fruit weight of the population 1 after one generation of selection is therefore predicted to be: New mean = Unselected mean + predicted response = 60g + 10g = 70g

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