Q: If a couple, both heterozygous for cystic fibrosis, have two children, what is the probability that both children will be carriers but not affected?

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

Question 1

In a pedigree, which symbol is used to represent an unaffected female?

Accepted Answer

An open circle

Question 2

A man without a chin dimple (autosomal dominant trait) marries a woman with a chin dimple whose mother did not have a dimple. What proportion of their children are likely to have a chin dimple?

Accepted Answer

$\frac{1}{2}$

Question 3

If a man with a chin dimple and a woman without a chin dimple have a child who lacks a dimple, what is the man's genotype?

Accepted Answer

Cc

Question 4

A man with a chin dimple and an undimpled woman have three children, all of whom have a chin dimple. What is the most likely genotype for the man?

Accepted Answer

CC, because all children must inherit a dominant allele

Question 5

Galactosemia is an autosomal recessive disease. If two heterozygous parents have fraternal twins, what is the probability that both twins will have galactosemia?

Accepted Answer

$\frac{1}{16}$

Question 6

If two heterozygous parents for galactosemia have identical twins, what is the probability that both twins will have galactosemia?

Accepted Answer

$\frac{1}{4}$

Question 7

A couple, both heterozygous for galactosemia, have four children (none are twins). What is the probability that none of the children will have galactosemia?

Accepted Answer

$\frac{27}{256}$

Question 8

A couple, both heterozygous for galactosemia, have four children (none are twins). What is the probability that at least one child will have galactosemia?

Accepted Answer

$\frac{229}{256}$

Question 9

Which of the following statements about X-linked recessive traits is correct?

Accepted Answer

Males only need one copy of the mutant allele to express the trait

Question 10

A woman with normal vision whose father is color-blind marries a color-blind man. What is the probability that their son will be color-blind?

Accepted Answer

$0$

Question 11

A woman with normal vision whose father is color-blind marries a color-blind man. What is the probability that their daughter will be color-blind?

Accepted Answer

$\frac{1}{2}$

Question 12

Which of the following is a key feature of autosomal dominant inheritance in a pedigree?

Accepted Answer

Affected individuals have at least one affected parent

Question 13

Cystic fibrosis is an autosomal recessive disorder. If two carriers have a child, what is the probability that the child will be affected?

Accepted Answer

$\frac{1}{4}$

Question 14

In a pedigree, how can you distinguish between autosomal and X-linked inheritance?

Accepted Answer

X-linked traits often show more affected males than females

Question 15

If a trait is autosomal recessive, what is the genotype of an individual who expresses the trait?

Accepted Answer

Homozygous recessive

Question 16

A pedigree shows a trait appearing in every generation. What is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 17

If 1% of X chromosomes in a population are mutant, what percentage of males will express the X-linked trait?

Accepted Answer

1%

Question 18

Which of the following is a consequence of cystic fibrosis at the cellular level?

Accepted Answer

Buildup of thick, sticky mucosal layer due to defective chloride ion channels

Question 19

A pedigree shows affected males passing a trait only to their daughters, never to their sons. What is the most likely mode of inheritance?

Accepted Answer

X-linked dominant

Question 20

If a couple, both heterozygous for cystic fibrosis, have two children, what is the probability that both children will be carriers but not affected?

Accepted Answer

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

Pedigree Analysis, Transmission Patterns, and Genetic Probability

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