Q: In a family, both parents are carriers for a recessive genetic disorder. What is the probability that their first two children will both be affected by the disorder? (Assume independent assortment.)

$$\left(\frac{1}{4}\right) \times \left(\frac{1}{4}\right) = \frac{1}{16}$$

Q: A couple, both of whom had a sibling with a recessive genetic disease, but neither parent nor themselves are affected. What is the probability that their child will have the disease? (Assume both are carriers with probability $$\frac{2}{3}$$ each.)

$$\frac{2}{3} \times \frac{2}{3} \times \frac{1}{4} = \frac{1}{9}$$

Question 1

Which of the following best describes the difference between a character and a trait in Mendelian genetics?

Accepted Answer

A character is a heritable feature that varies among individuals, while a trait is a specific variant of that character.

Question 2

Why were pea plants ideal for Mendel's genetic experiments?

Accepted Answer

They have a short generation time, produce large numbers of offspring, and mating can be controlled.

Question 3

Mendel's law of segregation states that:

Accepted Answer

The two alleles for a heritable character separate during gamete formation and end up in different gametes.

Question 4

A cross between two heterozygous pea plants (Pp x Pp) for flower color results in what expected phenotypic ratio in the offspring?

Accepted Answer

$$3:1$$

Question 5

If a plant with genotype Pp is crossed with a plant with genotype pp, what fraction of the offspring are expected to have the dominant phenotype?

Accepted Answer

$$\frac{1}{2}$$

Question 6

Which of the following scenarios best illustrates the law of independent assortment?

Accepted Answer

A dihybrid cross between two heterozygotes (YyRr x YyRr) produces offspring with new combinations of traits not found in either parent.

Question 7

In a family, both parents are carriers for a recessive genetic disorder. What is the probability that their first two children will both be affected by the disorder? (Assume independent assortment.)

Accepted Answer

$$\left(\frac{1}{4}ight) 	imes \left(\frac{1}{4}ight) = \frac{1}{16}$$

Question 8

Which of the following is an example of incomplete dominance?

Accepted Answer

A cross between red and white snapdragons produces pink offspring.

Question 9

A man with blood type AB and a woman with blood type O have children. Which blood types are possible in their offspring?

Accepted Answer

A and B only

Question 10

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple phenotypic traits.

Question 11

In Labrador retrievers, coat color is determined by two genes: one for pigment color (B = black, b = brown) and one for pigment deposition (E = color, e = no color). What is the expected phenotype of a dog with genotype bbEe?

Accepted Answer

Brown coat

Question 12

Which of the following is an example of a multifactorial disorder?

Accepted Answer

Heart disease, which is influenced by both genetic and environmental factors

Question 13

A pedigree shows a trait that appears in every generation and affects both males and females equally. What is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 14

Which of the following best explains why consanguineous matings increase the risk of recessive genetic disorders?

Accepted Answer

Close relatives are more likely to carry the same rare recessive alleles.

Question 15

A couple, both of whom had a sibling with a recessive genetic disease, but neither parent nor themselves are affected. What is the probability that their child will have the disease? (Assume both are carriers with probability $$\frac{2}{3}$$ each.)

Accepted Answer

$$\frac{2}{3} 	imes \frac{2}{3} 	imes \frac{1}{4} = \frac{1}{9}$$

Question 16

Which of the following is an example of codominance?

Accepted Answer

A person with AB blood type expresses both A and B antigens equally.

Question 17

Which of the following best describes polygenic inheritance?

Accepted Answer

Multiple genes contribute additively to a single phenotype, such as human height.

Question 18

If a genetic counselor uses the multiplication rule to calculate the probability of a child inheriting two independent recessive traits, which formula should they use?

Accepted Answer

$$P(A 	ext{ and } B) = P(A) 	imes P(B)$$

Question 19

A testcross is used to determine the genotype of an individual with a dominant phenotype. Which result would indicate the individual is heterozygous?

Accepted Answer

Some offspring display the recessive phenotype.

Question 20

Which of the following best explains why dominant alleles are not necessarily more common than recessive alleles in a population?

Accepted Answer

Allele frequency is determined by evolutionary forces, not dominance.

Ch 14 Mendel and the Gene Idea: Principles of Inheritance

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