Question 1

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

Accepted Answer

$H^2$ is the proportion of phenotypic variance explained by genetic variance, calculated as $H^2 = \frac{V_G}{V_P}$

Question 2

If all phenotypic variation in a trait is due to environmental factors, what is the value of broad sense heritability ($H^2$)?

Accepted Answer

$H^2 = 0$

Question 3

In a study of blind cavefish, the total phenotypic variance in eye size ($V_P$) is $0.563$ and the environmental variance ($V_E$) is $0.057$. What is the broad sense heritability ($H^2$)?

Accepted Answer

$H^2 = \frac{0.506}{0.563} = 0.899$

Question 4

When comparing monozygotic (MZ) and dizygotic (DZ) twins, which formula correctly estimates the genetic variance ($V_G$) using their phenotypic variances ($V_P$ for DZ and $V_E$ for MZ)?

Accepted Answer

$V_G = 2(V_P^{DZ} - V_E^{MZ})$

Question 5

A researcher measures the variance in height among monozygotic twins as $15\ \mathrm{cm}^2$ and among dizygotic twins as $25\ \mathrm{cm}^2$. What is the estimated heritability ($H^2$) of height in this population?

Accepted Answer

$H^2 = \frac{20}{25} = 0.80$

Question 6

Which of the following is a major limitation of using twin studies to estimate heritability?

Accepted Answer

Monozygotic twins may share more similar environments than dizygotic twins, inflating estimates of genetic variance.

Question 7

In a population, the phenotypic variance ($V_P$) for a trait is $100$, and the genetic variance ($V_G$) is $60$. What is the broad sense heritability ($H^2$)?

Accepted Answer

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

Question 8

Which scenario would result in a broad sense heritability ($H^2$) value closest to 1?

Accepted Answer

All phenotypic variation is due to genetic differences.

Question 9

Why is it important to consider both genetic and environmental variance when studying quantitative traits?

Accepted Answer

Both contribute to the total phenotypic variance, and ignoring one can lead to inaccurate estimates of heritability.

Question 10

A trait has a phenotypic variance ($V_P$) of $0.8$ and an environmental variance ($V_E$) of $0.2$. What is the genetic variance ($V_G$) and broad sense heritability ($H^2$)?

Accepted Answer

$V_G = 0.6$, $H^2 = 0.75$

Question 11

In a twin study, why might the environmental variance ($V_E$) be greater for dizygotic twins than for monozygotic twins?

Accepted Answer

Dizygotic twins may experience more genetic differences, which can interact with the environment to increase $V_E$.

Question 12

If the concordance rate for a disease is 60% in monozygotic twins and 25% in dizygotic twins, what does this suggest about the disease?

Accepted Answer

There is a significant genetic component to the disease.

Question 13

Which of the following best explains why genome-wide association studies (GWAS) are used in humans instead of traditional breeding experiments?

Accepted Answer

Breeding experiments are not ethical or feasible in humans, so GWAS uses natural genetic variation in populations.

Question 14

A GWAS identifies a genetic marker associated with a disease. Which statement is most accurate?

Accepted Answer

The marker is associated with the disease, but may not be the causal variant.

Question 15

Which of the following equations correctly represents the relationship between phenotypic variance ($V_P$), genetic variance ($V_G$), and environmental variance ($V_E$)?

Accepted Answer

$V_P = V_G + V_E$

Question 16

In a population, if $V_G = 0$ and $V_E = 0.5$, what is the value of $H^2$?

Accepted Answer

$H^2 = 0$

Question 17

A researcher finds that the concordance rate for a trait is much higher in monozygotic twins than in dizygotic twins. What does this imply?

Accepted Answer

Genetic factors play a significant role in the expression of the trait.

Question 18

Which of the following is a potential confounding factor when interpreting twin studies for heritability?

Accepted Answer

Monozygotic twins may be treated more similarly than dizygotic twins, increasing shared environmental effects.

Question 19

If a trait has $H^2 = 0.8$, what does this mean in practical terms?

Accepted Answer

80% of the phenotypic variance in the population is due to genetic differences.

Ch 19b: Genetic Analysis of Quantitative Traits: Calculating Heritability

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