Question 1

A geneticist observes that a heterozygote for a certain gene produces a phenotype that is intermediate between the two homozygotes. Which inheritance pattern best explains this observation, and what is the molecular basis for this pattern?

Accepted Answer

Incomplete dominance; 50% of the functional protein produced by the heterozygote is not sufficient to produce the same phenotype as the homozygous dominant.

Question 2

A woman is heterozygous for the polydactyly allele (an autosomal dominant trait), but she has a normal number of fingers and toes. What genetic concept does this illustrate?

Accepted Answer

Incomplete penetrance

Question 3

In a population, 80% of individuals with the genotype for a dominant trait express the phenotype, while 20% do not. What is the penetrance of this trait?

Accepted Answer

$$80\%$$

Question 4

A cross between two heterozygous Manx cats (Mm x Mm) produces offspring in the ratio 2 Manx : 1 normal tail. Which genotype is lethal, and what is the expected proportion of lethal embryos?

Accepted Answer

MM; $$\frac{1}{4}$$

Question 5

A man with blood type AB and a woman with blood type O have a child. What is the probability that their child will have blood type A?

Accepted Answer

$$0.5$$

Question 6

Which of the following best describes the molecular explanation for the heterozygote advantage observed in sickle-cell anemia?

Accepted Answer

Heterozygotes produce both normal and sickle hemoglobin, and their red blood cells are more likely to rupture when infected by Plasmodium, reducing malaria propagation.

Question 7

A cross between two true-breeding white-flowered sweet pea plants (genotypes CCpp and ccPP) produces all purple F1 offspring. When these F1 plants are self-fertilized, the F2 generation shows a 9:7 ratio of purple to white flowers. What genetic phenomenon explains the appearance of purple flowers in the F1 generation?

Accepted Answer

Complementation

Question 8

In rodents, coat color is determined by two genes: A (agouti) and C (pigment production). The cross AaCc x AaCc produces offspring in a 9 agouti : 3 black : 4 albino ratio. Which genotype(s) result in the albino phenotype?

Accepted Answer

Any genotype with cc, regardless of the A gene

Question 9

A woman who is a carrier for Duchenne muscular dystrophy (X-linked recessive) has children with a man who is unaffected. What is the probability that their son will be affected?

Accepted Answer

$$0.25$$

Question 10

Which of the following is an example of a sex-influenced trait?

Accepted Answer

Scurs (hornlike growths) in cattle, where the allele is dominant in males but recessive in females

Question 11

A gene knockout experiment in mice shows no phenotypic effect unless a second, related gene is also knocked out. What genetic concept does this illustrate?

Accepted Answer

Gene redundancy

Question 12

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple phenotypic traits

Question 13

A temperature-sensitive lethal allele in Drosophila causes death only at $$30^\circC $$but not at $$22^\circC. $$What type of allele is this?

Accepted Answer

Conditional lethal allele

Question 14

Which of the following is true about codominance, as seen in human ABO blood types?

Accepted Answer

The heterozygote expresses both A and B antigens on the surface of red blood cells.

Question 15

A plant with genotype TtVv is crossed with another TtVv plant for capsule shape, where T and V are functionally redundant. What is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$15:1$$

Question 16

Which of the following best explains why a person with cystic fibrosis may have thick mucus in the lungs, salty sweat, and poor weight gain?

Accepted Answer

The CFTR gene is pleiotropic, affecting multiple tissues and physiological processes.

Question 17

Which of the following is a possible molecular explanation for a dominant mutant allele?

Accepted Answer

Gain-of-function mutation, where the mutant protein acquires a new or abnormal function.

Question 18

A cross between two agouti rats (AaCc x AaCc) produces some albino offspring. Which gene is epistatic to the other, and why?

Accepted Answer

The C gene is epistatic to the A gene because cc masks the effect of A, resulting in albino regardless of the A genotype.

Question 19

Which of the following best describes the difference between penetrance and expressivity?

Accepted Answer

Penetrance is the proportion of individuals with a genotype who express the phenotype; expressivity is the degree to which the phenotype is expressed among those who show it.

Question 20

A woman with genotype IAi and a man with genotype IBi have children. What is the probability that their child will have blood type AB?

Accepted Answer

$$0.25$$

Extensions of Mendelian Inheritance: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards