Q: In a twin study, monozygotic twins have a correlation coefficient of 0.8 for a trait, while dizygotic twins have a correlation of 0.4. What is the estimated heritability ($$h^2) of $$the trait?

$$h^2 = 2$$ \times (r_{MZ} - r_{DZ}) = 2 \times (0.8 - 0.4) = 0.8$$

Question 1

Which of the following best describes a quantitative trait?

Accepted Answer

A trait that shows continuous variation and is influenced by multiple genes and environmental factors.

Question 2

If the phenotypic variance ($$V_P) in a $$population is 100, and the genetic variance ($$V_G) is 40$$, what is the broad-sense heritability ($$H^2$$)?

Accepted Answer

$$H^2$$ = \frac{V_G}{V_P} = \frac{40}{100} = 0.4$$

Question 3

Which scenario would most likely result in a high heritability estimate for human height?

Accepted Answer

A population with diverse genetic backgrounds and similar environments.

Question 4

In a twin study, monozygotic twins have a correlation coefficient of 0.8 for a trait, while dizygotic twins have a correlation of 0.4. What is the estimated heritability ($$h^2) of $$the trait?

Accepted Answer

$$h^2 = 2$$ 	imes (r_{MZ} - r_{DZ}) = 2 	imes (0.8 - 0.4) = 0.8$$

Question 5

Which of the following statements about heritability is TRUE?

Accepted Answer

Heritability describes the proportion of phenotypic variance explained by genetic variance in a specific population and environment.

Question 6

A plant breeder selects the tallest plants from a population to breed. After several generations, the average height increases, but there is still variation among the plants. What is the most likely explanation for the remaining variation?

Accepted Answer

Environmental factors continue to influence plant height.

Question 7

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

Accepted Answer

$$V_P = V_G + V_E$$

Question 8

A researcher is mapping a quantitative trait using GWAS. What is a limitation of this approach?

Accepted Answer

GWAS does not necessarily identify the causal genetic variants.

Question 9

If a trait is influenced by 3 genes, each with two alleles, how many possible phenotypes can be observed (assuming additive effects)?

Accepted Answer

7 (using Pascal's rule: $$2n+1$$ where $$n=3)$$

Question 10

Which of the following is an example of a gene x environment interaction?

Accepted Answer

A plant with a genotype for tall height grows short due to poor soil quality.

Question 11

Which of the following would NOT increase the number of observed phenotypes for a quantitative trait?

Accepted Answer

Decreasing the number of genes controlling the trait.

Question 12

A population of plants has a mean corolla length of 5 cm and a standard deviation of 1 cm. What is the variance?

Accepted Answer

$$s^2$$ = $$(1)^2 = 1$

Question 13

Which of the following best explains why pure-breeding 'short' plants still show variation in corolla length?

Accepted Answer

Environmental variation affects the phenotype.

Question 14

Which of the following is NOT a reason for continuous variation in a quantitative trait?

Accepted Answer

Single-gene inheritance with complete dominance.

Question 15

Which of the following is a correct statement about Mendelian ratios and quantitative traits?

Accepted Answer

Quantitative traits often show continuous variation and do not follow Mendelian ratios.

Question 16

A population has a mean height of 175 cm, a variance of 25, and a standard deviation of 5. Which value represents the most common height?

Accepted Answer

Mode

Question 17

Which of the following is an exception to Mendelian inheritance observed in quantitative traits?

Accepted Answer

Epistasis

Question 18

If a trait has low heritability in a population, what does this imply?

Accepted Answer

Most of the phenotypic variation is due to environmental differences.

Question 19

Which of the following is a correct application of the concept of additive traits?

Accepted Answer

Each allele contributes a fixed amount to the phenotype, resulting in a range of possible phenotypes.

Question 20

Which of the following best describes the use of QTL mapping in genetic analysis?

Accepted Answer

It maps quantitative traits to genomic regions associated with phenotypic variation.

Ch 19a: Genetic Analysis of Quantitative Traits: Introduction and Key Concepts

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