Question 1

Which of the following statements best explains why autosomal dominant disorders, such as Huntington's disease, can persist in a population even though they are often fatal?

Accepted Answer

The symptoms of autosomal dominant disorders often appear after reproductive age, allowing affected individuals to pass on the allele before knowing they have the disorder.

Question 2

A couple, both of whom are carriers for an autosomal recessive disorder, are planning to have children. What is the probability that their first child will be affected by the disorder? Use a Punnett square to justify your answer.

Accepted Answer

25% chance, because the Punnett square shows that $$\frac{1}{4} of $$the offspring will be homozygous recessive.

Question 3

Which of the following best describes the inheritance pattern of cystic fibrosis in humans?

Accepted Answer

Autosomal recessive, where only individuals with two recessive alleles ($$aa) $$are affected.

Question 4

A pedigree shows a trait that appears in every generation and affects males and females equally. Which inheritance pattern is most likely?

Accepted Answer

Autosomal dominant

Question 5

Which of the following is an example of pleiotropy?

Accepted Answer

Marfan syndrome, where a single gene mutation affects the skeleton, eyes, and cardiovascular system.

Question 6

A woman with type AB blood ($$I^A I^B) $$and a man with type O blood ($$ii) $$have a child. What are the possible blood types of their child?

Accepted Answer

Type A or Type B

Question 7

Which of the following best explains why males are more likely than females to express X-linked recessive disorders?

Accepted Answer

Males have only one X chromosome, so a single recessive allele on the X will result in the disorder.

Question 8

A man with hemophilia (an X-linked recessive disorder) marries a woman who is a carrier. What is the probability that their daughter will have hemophilia?

Accepted Answer

50%, because the daughter must inherit the affected X from her father and has a 50% chance of inheriting the affected X from her mother.

Question 9

Which of the following is an example of incomplete dominance?

Accepted Answer

A cross between red-flowered and white-flowered snapdragons produces pink-flowered offspring.

Question 10

Which of the following best describes polygenic inheritance?

Accepted Answer

A trait is controlled by two or more sets of alleles, each with an additive effect on the phenotype.

Question 11

A woman who is a carrier for colorblindness (X-linked recessive) and a man with normal vision have a son. What is the probability that their son will be colorblind?

Accepted Answer

50%, because the son has a 50% chance of inheriting the X chromosome carrying the colorblind allele from his mother.

Question 12

Which of the following scenarios best illustrates the concept of incomplete penetrance?

Accepted Answer

A person inherits a dominant allele for polydactyly but does not exhibit extra fingers or toes.

Question 13

Which of the following best explains why type O blood is considered the universal donor?

Accepted Answer

Type O blood cells lack A and B antigens, so they are not recognized as foreign by any recipient's immune system.

Question 14

A pedigree shows that two unaffected parents have an affected child. Which inheritance pattern is most likely responsible for the trait?

Accepted Answer

Autosomal recessive

Question 15

Which of the following is a real-world example of environmental influence on a polygenic trait?

Accepted Answer

Children in post-World War II Europe experienced stunted height due to malnutrition, despite their genetic potential for tall stature.

Question 16

Which of the following best describes codominance?

Accepted Answer

Both alleles are fully expressed in the heterozygote, as seen in type AB blood ($$I^A I^B).$$

Question 17

A man with normal vision and a woman who is a carrier for an X-linked recessive disorder have a daughter. What is the probability that their daughter will be affected?

Accepted Answer

0%, because the daughter would need to inherit two copies of the recessive allele (one from each parent), but the father is not affected.

Question 18

Which of the following best explains why close relatives who reproduce are more likely to have children affected by autosomal recessive disorders?

Accepted Answer

Close relatives are more likely to carry the same recessive allele, increasing the chance their children will inherit two copies.

Question 19

Which of the following is NOT a feature of X-linked inheritance?

Accepted Answer

The Y chromosome carries many genes unrelated to sex determination.

Beyond Mendelian Inheritance: Human Genetic Disorders and Complex Patterns

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