Question 1

Which of the following best describes the multiple-gene hypothesis as supported by Edward East’s tobacco experiment?

Accepted Answer

Quantitative traits are controlled by multiple genes, each contributing a small additive effect, and environmental factors also influence the phenotype.

Question 2

In the context of quantitative genetics, how is total phenotypic variance ($$V_P) $$partitioned?

Accepted Answer

$$V_P = V_G + V_E$$

Question 3

A population of plants shows a bell-shaped distribution for height. What does this indicate about the genetic control of this trait?

Accepted Answer

The trait is likely controlled by multiple genes and influenced by environmental factors.

Question 4

Which of the following scenarios best illustrates a gene–environment interaction?

Accepted Answer

A single genotype produces a range of phenotypes depending on environmental conditions.

Question 5

In Edward East’s experiment, the F₁ generation of tobacco plants showed a narrow distribution of corolla lengths. What was the main source of variation in this generation?

Accepted Answer

Environmental variation

Question 6

Which equation correctly represents the relationship between phenotypic variance, genetic variance, and environmental variance?

Accepted Answer

$$V_P = V_G + V_E$$

Question 7

A researcher observes that the difference between two parental strains of a plant is mainly due to genetic differences, while the variation among individuals within each strain is mainly due to:

Accepted Answer

Environmental effects

Question 8

Which of the following best describes the distribution of phenotypes in the F₂ generation of a cross between two pure-breeding lines for a quantitative trait?

Accepted Answer

A broad, continuous distribution due to both genetic and environmental variation

Question 9

If a trait is influenced by additive alleles, what is the expected effect on the phenotype?

Accepted Answer

Each allele contributes a small, cumulative effect to the phenotype.

Question 10

Which of the following statements about normal distributions in quantitative genetics is TRUE?

Accepted Answer

Quantitative traits controlled by multiple genes and environmental factors often show a normal (bell-shaped) distribution in populations.

Question 11

A population shows the same mean for a trait in two different environments, but one environment has a much larger variance. What does this suggest?

Accepted Answer

Environmental factors in the second environment increase phenotypic variance.

Question 12

Which of the following is an example of a non-additive genetic effect?

Accepted Answer

Dominance and epistasis

Question 13

If $$V_P = 20$$ and $$V_E = 5$$, what is the genetic variance ($$V_G$$)?

Accepted Answer

$$V_G = 15$$

Question 14

Which of the following best explains why the underlying genotype is difficult to determine from phenotype in quantitative traits?

Accepted Answer

Multiple genes and environmental factors contribute to the phenotype, creating overlapping phenotypic distributions.

Question 15

In a scenario with substantial gene–environment interaction, what is the expected pattern of phenotypic expression?

Accepted Answer

Wide phenotypic ranges and significant overlap between genotypes

Question 16

Which statistical tools are most commonly used to describe variation in quantitative traits?

Accepted Answer

Mean and variance

Question 17

A researcher measures the corolla length in a large sample of tobacco plants and finds a bell-shaped curve. What does this indicate about the trait?

Accepted Answer

It is a quantitative trait influenced by multiple genes and environmental factors.

Question 18

Which of the following best describes the effect of increasing the number of genes contributing to a quantitative trait?

Accepted Answer

The phenotypic distribution becomes more continuous and bell-shaped.

Question 19

If a population’s phenotypic variance is entirely due to environmental factors, what would you expect about the genetic variance?

Accepted Answer

Genetic variance ($$V_G) $$would be zero.

Quantitative Genetics: Multifactorial and Complex Traits

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