Question 1

According to the multiple-gene hypothesis, what is the expected phenotypic ratio in the F2 generation when two heterozygotes for two additive gene pairs are crossed?

Accepted Answer

1:4:6:4:1

Question 2

If a quantitative trait is controlled by three additive gene pairs, how many distinct phenotypic categories are expected in the F2 generation?

Accepted Answer

$$2n + 1 = 7$$

Question 3

Which formula is used to estimate the number of polygenes (n) contributing to a quantitative trait based on the ratio of F2 individuals expressing either extreme phenotype?

Accepted Answer

$$\frac{1}{4^n}$$

Question 4

A population of cattle has a narrow-sense heritability ($$h^2) $$for milk yield of 44%. What does this value indicate?

Accepted Answer

44% of the phenotypic variance in milk yield is due to additive genetic variance.

Question 5

Which component of genotypic variance is most important for predicting the response to artificial selection?

Accepted Answer

Additive variance ($$V_A)$$

Question 6

In the context of artificial selection for increased oil content in corn, what does a realized heritability value of 0.34 at generation 25 mean?

Accepted Answer

34% of the variation in oil content is due to genetic differences and can be passed to the next generation.

Question 7

Which equation represents broad-sense heritability ($$H^2$$)?

Accepted Answer

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

Question 8

A tomato breeder selects for larger fruit size over several generations. Which type of heritability is most useful for predicting the success of this selection?

Accepted Answer

Narrow-sense heritability ($$h^2)$$

Question 9

If the mean tomato weight in a population is 10 oz and the sum of all individual weights is 200 oz for 20 tomatoes, what is the calculated mean?

Accepted Answer

$$\bar{x} = \frac{\sum x_i}{n} = \frac{200}{20} = 10$$

Question 10

Which of the following best describes the effect of increasing the number of additive gene pairs on the distribution of phenotypes in the F2 generation?

Accepted Answer

The distribution becomes more continuous and bell-shaped.

Question 11

In a population where the phenotypic variance ($$V_P) is 100 $$and the genotypic variance ($$V_G) is 60$$, what is the broad-sense heritability ($$H^2$$)?

Accepted Answer

$$H^2$$ = \frac{60}{100} = 0.6$$

Question 12

Which scenario would likely result in the slowest response to artificial selection?

Accepted Answer

A trait with low narrow-sense heritability and high environmental variance.

Question 13

What is the primary reason that traits of economic importance, such as milk yield in cattle, are often polygenic and multifactorial?

Accepted Answer

They are influenced by many genes and environmental factors.

Question 14

Which of the following is NOT a component of genotypic variance?

Accepted Answer

Environmental variance ($$V_E)$$

Question 15

If a trait in chickens has a heritability ($$h^2) of 20$$%, what does this imply about the effectiveness of selection for this trait?

Accepted Answer

Selection will be relatively ineffective because most variation is due to environmental factors.

Question 16

A breeder observes that the variance in tomato weight is much higher in the F2 generation than in the F1 generation. What is the most likely explanation?

Accepted Answer

The F2 generation has greater genetic diversity due to recombination.

Question 17

Which of the following best explains why the beefsteak tomato is much larger than its wild ancestor?

Accepted Answer

Artificial selection for increased fruit size over many generations.

Question 18

In the context of quantitative genetics, what is meant by 'additive alleles'?

Accepted Answer

Alleles that contribute equally and cumulatively to the phenotype.

Question 19

If the heritability of human height is 0.65, what does this mean in practical terms?

Accepted Answer

65% of the variation in height is due to genetic differences among individuals.

Quantitative Genetics: Polygenic Inheritance, Heritability, and Artificial Selection

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