Q: If a trait is controlled by three additive genes, how many distinct phenotypic categories are expected?

$$2n + 1 = 2 \times 3 + 1 = 7$$

Question 1

Which of the following best distinguishes a continuous (quantitative) trait from a discontinuous (Mendelian) trait?

Accepted Answer

Continuous traits show a range of phenotypes, while discontinuous traits have distinct categories.

Question 2

A researcher observes 9 different shades of fur color in a population of rabbits. Using the formula $$2n + 1 = 	ext{number of phenotypic categories}$$, how many polygenes are likely involved in determining fur color?

Accepted Answer

$$n = 4$$

Question 3

Which of the following is an example of a quantitative trait in humans?

Accepted Answer

Height

Question 4

What is the main difference between polygenic and multifactorial traits?

Accepted Answer

Polygenic traits are controlled by many genes, while multifactorial traits are influenced by both genes and the environment.

Question 5

In a cross between two wheat plants, one with genotype $$A_1A_1B_1B_1 ($$dark red) and one with $$A_2A_2B_2B_2 ($$white), what is the expected phenotype of the $$F_1$$ generation if the alleles are additive?

Accepted Answer

Intermediate color (dark pink)

Question 6

Which statement about additive alleles is correct?

Accepted Answer

Each additive allele contributes equally to the intensity of the phenotype.

Question 7

If a trait is controlled by three additive genes, how many distinct phenotypic categories are expected?

Accepted Answer

$$2n + 1 = 2 	imes 3 + 1 = 7$$

Question 8

Which of the following best describes the effect of increasing the number of additive genes controlling a trait?

Accepted Answer

The phenotypic distribution becomes more continuous and bell-shaped.

Question 9

A plant breeder crosses two heterozygous plants for three additive loci ($$AaBbCc 	imes AaBbCc). $$What is the expected frequency of the most extreme phenotype (all dominant or all recessive alleles) in the $$F_2$$ generation?

Accepted Answer

$$\frac{1}{64}$$

Question 10

Which of the following statements about polygenic traits is true?

Accepted Answer

They are influenced by multiple genes, each contributing a small additive effect.

Question 11

A scientist finds 11 different phenotypic categories for a trait in a population. Using the formula $$2n + 1 = 11$$, how many genes are likely involved?

Accepted Answer

5

Question 12

Which of the following is a real-world example of a quantitative trait in agriculture?

Accepted Answer

Milk production in dairy cows

Question 13

In the context of quantitative genetics, what is a polygene?

Accepted Answer

A gene that contributes to a quantitative trait along with other genes

Question 14

Which of the following best explains why quantitative traits are harder to study than single-gene traits?

Accepted Answer

There is not a one-to-one mapping of gene to trait, and many genes contribute to the phenotype.

Question 15

A population of mice shows 7 different eye colors. Using the formula $$2n + 1 = 7$$, how many polygenes are involved?

Accepted Answer

3

Question 16

Which of the following is NOT a characteristic of additive alleles?

Accepted Answer

They always show complete dominance over nonadditive alleles.

Question 17

If a trait is controlled by four additive genes, what is the frequency of the most extreme phenotype in the $$F_2$$ generation?

Accepted Answer

$$\frac{1}{256}$$

Question 18

Which of the following best describes the inheritance pattern of polygenic traits at individual loci?

Accepted Answer

Each locus follows Mendelian inheritance, but the overall trait shows continuous variation.

Question 19

A cross between two plants with genotypes $$AABB ($$red) and $$aabb ($$white) produces $$F_1$$ offspring with genotype $$AaBb ($$pink). What does this illustrate about the alleles involved?

Accepted Answer

Additive alleles at two loci contribute to an intermediate phenotype.

Question 20

Which of the following would you expect to see as the number of additive genes controlling a trait increases?

Accepted Answer

A smoother, more continuous distribution of phenotypes.

Quantitative Genetics: Additive Alleles and Polygenic Inheritance

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