11) Color blindness is caused by an X-linked recessive gene. A color-blind man and a woman with normal vision whose father was color blind have a son. The probability that their son is color blind is:

A) 0.25 (or 25 percent).

B) 0.50 (or 50 percent).

C) 0.75 (or 75 percent).

D) 1.00 (or 100 percent).

E) none of these.

12) Who is a “carrier” of X-linked disorders, such as hemophilia and color blindness?

A) a person who has the X-linked disorder

B) a heterozygous female who is normal but carries one nonfunctioning allele

C) a homozygous female who carries the normal alleles

D) a male who carries the nonfunctioning allele

E) a male who carries the functioning allele

13) An autosomal recessive disorder:

A) requires that only one parent be a carrier.

B) displays its symptoms only in heterozygotes.

C) is more frequent in males than females.

D) will appear only in children of parents who both carry the gene.

E) is dominant in females.

14) Genes not found on the sex chromosomes will be found on:

A) X chromosomes.

B) Y chromosomes.

C) autosomes.

D) centrosomes.

15) If a disease is caused by a dominant allele, it means that a person with the disease:

A) will always pass it on to all their children.

B) will pass it on to one-fourth of their children.

C) must be homozygous dominant for the allele.

D) must be heterozygous for the allele.

E) could be either homozygous or heterozygous for the allele.

16) A person who is heterozygous for the Huntington disease (HD) allele has offspring with someone who does not have HD. What proportion of their children will have HD?

A) 1/16

B) 1/10

C) 1/8

D) 1/4

E) 1/2

17) A person with an inherited disorder has children with a person who does not have the condition. Half the children have the disorder, both sons and daughters. How is this condition inherited?

A) autosomal dominant

B) autosomal recessive

C) X-linked dominant

D) X-linked recessive

E) aneuploidy

18) What condition is caused by a dominant allele of a single gene?

A) Down syndrome

B) sickle-cell anemia

C) Huntington disease

D) color blindness

E) Turner syndrome

19) A person who has a recessive disorder but does not have the disorder him or herself is said to be a/an:

A) aneuploid.

B) aberration.

C) carrier.

D) hybrid.

20) What is the connection between sickle-cell anemia and malaria?

A) Both are X-linked.

B) Both are autosomal recessive.

C) Both are dominant.

D) Heterozygotes for malaria have some resistance to sickle-cell anemia.

E) Heterozygotes for sickle-cell anemia have some resistance to malaria.