Question

You are an almond grower and want to determine whether almond size (measured as shelled almond weight) is a heritable trait. A survey of 800 trees from several groves indicates that the average shelled almond weight is 5.71 g. You select the 40 trees producing the biggest almonds (average shelled almond weight of 6.48 g), then cross-pollinate the flowers from these trees. You plant the almonds produced by these flowers and when the resulting trees reach maturity, you measure the size of their almonds and find that the average shelled almond weight is 5.85 g.
1. Calculate the selection differential.
2. Calculate the response to selection.
3. Calculate heritability (h2).
4. If you were to carry out this breeding program for multiple generations would you expect to see almond production to be strongly influenced by genetics, environment, or a combination? Explain.

Answer 1

Answer: 1. S = 0.77

              2. R = 0.14

Explanation:

1. Selection differential is the difference between the population mean and the average of the selected parents. Its symbol is S.

S = mean of selected parents - population mean

S = 6.48 - 5.71

S = 0.77

2. Response to Selection is how much gain you make when crossing over selected parents. Its symbol is R.

R = mean of offspring of selected parents - population mean

R = 5.85 - 5.71

R = 0.14

3. Heritability is, basically, a statistical variable that shows how much the variation in a trait is due to genetic factors. Its symbol is h².

To calculate it, use Breeder's Equation:

R = h²S

$h^{2}=\frac{R}{S}$

$h^{2}=\frac{0.14}{0.77}$

h² = 0.18

4. You would expect the production to be strongly influenced by environment, because heritability lies between 0 and 1. Low heritability means there is low level of resemblance between offspring and parents. As this program heritability is low, the resemblance is small, which means the characteristics are influenced mostly by the enviroment.