Question 1

In the pedigree shown, filled symbols represent individuals affected by Waardenburg syndrome. Based on the pattern of affected individuals across generations, which mode of inheritance is most likely for Waardenburg syndrome?

Accepted Answer

Autosomal dominant

Question 2

If both parents are heterozygous carriers for an autosomal recessive disorder, what is the probability that their child will be affected? Use the formula for Mendelian inheritance.

Accepted Answer

$$ \frac{1}{4} $$

Question 3

A man affected by an X-linked recessive disorder marries a woman who is not a carrier. What is the expected outcome for their children?

Accepted Answer

All sons will be unaffected, all daughters will be carriers.

Question 4

Which of the following statements best describes Y-linked inheritance?

Accepted Answer

Trait is passed from father to all sons and never skips generations.

Question 5

In a pedigree, if a trait appears in both sexes with equal frequency and does not skip generations, which mode of inheritance is most likely?

Accepted Answer

Autosomal dominant

Question 6

A young couple each has a sibling with cystic fibrosis (an autosomal recessive disorder), but neither is affected. What is the probability that their child will have cystic fibrosis?

Accepted Answer

$$ \frac{1}{9} $$

Question 7

If a trait is X-linked dominant, which of the following is true regarding affected fathers?

Accepted Answer

All daughters will be affected, no sons will be affected.

Question 8

Which equation best represents the probability that a child will be affected by an autosomal dominant disorder if one parent is heterozygous and the other is unaffected?

Accepted Answer

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

Question 9

In twin studies, concordance is defined as:

Accepted Answer

The percentage of twin pairs that both express a trait.

Question 10

Table 6.2 shows that the concordance for cancer is 12% in monozygotic twins and 15% in dizygotic twins. What does this suggest about the cause of cancer?

Accepted Answer

Cancer is mostly linked to environmental factors.

Question 11

Which of the following is NOT a characteristic of autosomal recessive inheritance?

Accepted Answer

Trait is passed from father to all sons.

Question 12

A woman who is a carrier for an X-linked recessive disorder has children with a man who is unaffected. What proportion of their sons will be affected?

Accepted Answer

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

Question 13

Which statement best describes the inheritance pattern of classic hemophilia in European royal families?

Accepted Answer

X-linked recessive

Question 14

If a trait is autosomal dominant, what is the expected proportion of affected offspring when one parent is heterozygous and the other is unaffected?

Accepted Answer

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

Question 15

Which of the following is a characteristic of X-linked recessive inheritance?

Accepted Answer

Trait is never passed from father to son.

Question 16

A pedigree shows a trait that only affects males and is passed from father to all sons. What is the most likely mode of inheritance?

Accepted Answer

Y-linked

Question 17

Which formula would you use to calculate the probability that a child will inherit an autosomal recessive disorder from two heterozygous parents?

Accepted Answer

$$ P = \frac{1}{4} $$

Question 18

Which of the following best describes the difference between monozygotic and dizygotic twins?

Accepted Answer

Monozygotic twins are genetically identical, dizygotic twins are not.

Question 19

In studies of adoptees, which factor is shown to have a genetic influence?

Accepted Answer

Body mass index

Question 20

If a trait is X-linked dominant, what is the expected outcome for the children of an affected mother (heterozygous) and an unaffected father?

Accepted Answer

Half of sons and half of daughters will be affected.

Human Genetics and Pedigree Analysis: Patterns of Inheritance and Twin Studies

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