The following variances were calculated for two traits in a herd of hogs.

Which of the two traits will respond best to selection by a breeder? Why?

What kind of heritability estimates (broad sense or narrow sense) are obtained from human twin studies?

Corn plants from a test plot are measured, and the distribution of heights at 10-cm intervals is recorded in the following table: 

 Height (cm)   Plants (no.)    

100          20    

110          60    

120          90    

130         130    

140         180   

 150         120    

160          70    

170         50    

180         40 

Calculate 

(a) the mean height, 

(b) the variance, 

(c) the standard deviation, and 

(d) the standard error of the mean. 

Plot a rough graph of plant height against frequency. Do the values represent a normal distribution? Based on your calculations, how would you assess the variation within this population?

In selective breeding experiments, it is frequently observed that the strains respond to artificial selection for many generations, with the selected phenotype changing in the desired direction. Often, however, the response to artificial selection reaches a plateau after many generations, and the phenotype no longer changes as it did in past generations. Once a plateau has been reached, is the heritability of the trait very high or is it very low? Explain.

The following variances were calculated for two traits in a herd of hogs.

Calculate broad-sense (H²) and narrow-sense (h²) heritabilities for each trait in this herd.

The mean and variance of plant height of two highly inbred strains (P₁ and P₂) and their progeny (F₁ and F₂) are shown here.

  Strain  Mean (cm)  Variance 

   P₁     34.2        4.2

   P₂     55.3        3.8

   F₁     44.2        5.6

   F₂     46.3       10.3

Calculate the broad-sense heritability (H²) of plant height in this species.

A hypothetical study investigated the vitamin A content and the cholesterol content of eggs from a large population of chickens. The following variances (V) were calculated.

Which trait, if either, is likely to respond to selection?

A hypothetical study investigated the vitamin A content and the cholesterol content of eggs from a large population of chickens. The following variances (V) were calculated.

Calculate the narrow-sense heritability (h²) for both traits.

In Nicotiana, two inbred strains produce long (PL) and short (PS) corollas. These lines are crossed to produce F₁, and the F₁ are crossed to produce F₂ plants in which corolla length and variance are measured. The following table summarizes the mean and variance of corolla length in each generation. Calculate H² for corolla length in Nicotiana.