Question 1

Which of the following best describes additive genetic variance ($$V_A) in $$the context of quantitative genetics?

Accepted Answer

It is the variance due to the average effect of each allele that affects the trait, where each additional allele adds a consistent, predictable effect to the phenotype.

Question 2

A plant breeder selects parent plants with a mean height of 80 cm from a population with a mean height of 70 cm. The mean height of the offspring is 74 cm. What is the narrow-sense heritability ($$h^2) of $$plant height in this population?

Accepted Answer

$$h^2$$ = \frac{4}{10} = 0.4$$

Question 3

Which equation correctly represents the partitioning of total phenotypic variance ($$V_T) in a $$quantitative trait?

Accepted Answer

$$V_T = V_E + (V_A + V_D + V_I)$$

Question 4

If the narrow-sense heritability ($$h^2) of a $$trait is 0.8, what does this mean in a population?

Accepted Answer

80% of the variation in this population is due to additive genetic factors.

Question 5

A population of pigs has a mean back-fat thickness of 20 mm. Selected parents have a mean of 25 mm, and the offspring mean is 22 mm. What is the selection differential ($$S) $$and response to selection ($$R$$)?

Accepted Answer

$$S = 5 mm$$, $$R = 2 mm$$

Question 6

Which of the following scenarios best illustrates dominance variance ($$V_D$$)?

Accepted Answer

The heterozygote has the same phenotype as one homozygote, masking the other allele’s effect.

Question 7

Given the equation $$T_O = \mu + h^2$[(T_M + T_F)/2 - \mu]$$, what is the predicted offspring mean ($$T_O) if$$ $$\mu = 100$$, $$T_M = 110$$, $$T_F = 120$$, and $$h^2 = 0.4$?

Accepted Answer

$$T_O = 106$$

Question 8

Which of the following best describes broad-sense heritability ($$H^2$$)?

Accepted Answer

It measures the proportion of total phenotypic variation that is due to all genetic variation (additive, dominance, and epistatic).

Question 9

In a population, the selected parents have a mean of 40, the population mean is 30, and the offspring mean is 33. What is the heritability ($$h^2) of $$this trait?

Accepted Answer

$$h^2 = 0.3$

Question 10

If $$h^2 = 0.6$ and the midparent value is 10 cm above the population mean, what is the predicted offspring mean shift?

Accepted Answer

6 cm

Question 11

Which of the following is a real-world application of narrow-sense heritability ($$h^2$$)?

Accepted Answer

Predicting the response of a crop to artificial selection for increased yield.

Question 12

Which of the following statements about epistatic variance ($$V_I) is $$correct?

Accepted Answer

It arises from interactions among alleles at different genes, where one gene can mask or alter the expression of another.

Question 13

A trait in a population has $$H^2 = 0.7$ and h^2$ = 0.3. $$What does this indicate about the genetic architecture of the trait?

Accepted Answer

Non-additive genetic effects (dominance and epistasis) contribute substantially to the genetic variance.

Question 14

When a population responds to selection ($$R \u003e 0$$), what is happening at the genetic level?

Accepted Answer

The frequency of beneficial alleles in the population increases.

Question 15

Which of the following best explains why dominance and epistatic variance are not predictably transmitted to offspring?

Accepted Answer

Their effects depend on specific allele combinations that may not be inherited together.

Question 16

A breeder is interested in increasing egg production in poultry. The narrow-sense heritability ($$h^2) $$for egg production is 0.20. What does this suggest about the effectiveness of selection for this trait?

Accepted Answer

Selection will result in a modest response because only 20% of the variation is due to additive genetic factors.

Question 17

Which of the following formulas is used to estimate broad-sense heritability ($$H^2$$)?

Accepted Answer

$$H^2$$ = \frac{V_G}{V_T}$$

Question 18

A population of flowering plants has a mean petal number of 5. A plant with 6 petals is mated to a plant with 8 petals. If $$h^2 = 0.3$, what is the expected mean petal number in the offspring?

Accepted Answer

5.6

Heritability: Broad Sense and Narrow Sense in Quantitative Genetics

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