Number correct: 20
Number incorrect: 0
1. The most common phenotype in a natural population is referred to as the
a. genotype.
b. wild type.
Correct. The most common phenotype is the wild type.
c. autosome.
d. mutant phenotype.
e. locus.
2. Human males are much more likely to have hemophilia (a failure of blood to clot
properly) than human females. This is the case because
a. hemophilia is a contagious disease to which males are more susceptible.
b. the gene for hemophilia is carried on the Y chromosome.
c. the gene for hemophilia is carried on an autosome.
d. hemophilia is the wild type.
e. the gene for hemophilia is sex-linked.
Correct. A female would have to have the hemophilia gene on both of her X
chromosomes in order to be a hemophiliac. If a male has the gene for hemophilia on his X
chromosome he will have hemophilia.
3. In a particular species of mammal, black hair (B) is dominant to green hair (b) and red
eyes (R) are dominant to white eyes (r). If a BbRr individual is mated with a bbrr
individual, the expected phenotypic ratio of the offspring is 1 black-red:1 black-white:1
green-red:1 green-white. However, when you mate these individuals you find that the
phenotypic ratio of the offspring is 6 black-red:1 black-white:1 green-red:6 green-white.
What could account for this difference?
a. Green-haired individuals have a higher prenatal mortality than black-haired
individuals.
b. The genes for hair color and the genes for eye color are carried on different
chromosomes.
c. The expected results did not take genetic recombination into account.
d. The genes for both of these traits are carried on the autosomes.
e. The genes for hair color and eye color are linked.
Correct. This explains why the parental types occur more often than would be expected if
the traits assort at random.
4. In problem 3, the observed distribution of offspring was: black-red 1070; black-white
177; green-red 180; green-white 1072. Based on this data, what is the recombination
frequency?
a. 86 percent
b. 7
c. 17 percent
d. 14 percent
Correct. 177 + 180 = 357 recombinants. 357 recombinants/2499 total offspring x 100 =
14%.
e. 30 percent
5. How many map units is a recombination frequency of 5 percent equal to?
a. 2.5 centimorgans
b. 10 centimorgans
c. 5 centisturtevants
d. 5 percent
e. 5 centimorgans
Correct. A recombination frequency of 1 percent can be expressed as 1 centimorgan on a
genetic map.
6. A linkage map
a. orders genes on a chromosome based on recombination frequencies.
Correct. A linkage map is not a true representation of the actual distances between genes.
b. can only be constructed for sex chromosomes.
c. orders genes on a chromosome based on their location with respect to a stained band.
d. shows the ordering and exact spacing of genes on a chromosome.
e. predicts the probability that you will have a male or female child.
7. A male bee is
a. XY.
b. diploid.
c. ZZ.
d. ZW.
e. haploid.
Correct. In this haplo-diploid system the female bees are diploid.
8. What is the probability that a male will inherit an X-linked recessive allele from his
father?
a. 0
Correct. A male receives a Y chromosome from his father, not an X.
b. 25 percent
c. 50 percent
d. 75 percent
e. 100 percent
9. Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are
almost invariably boys, who usually die before the age of 20. Why is this disorder almost
never seen in girls?
a. Sex-linked traits are never seen in girls.
b. The allele is carried on the Y chromosome.
c. Nondisjunction occurs in males but not in females.
d. In order to express an X-linked recessive allele, a female must have two copies of
the allele.
Correct. Moreover, males carrying the allele have less of an opportunity to have
offspring.
e. A sex-linked allele cannot be passed from mother to daughter.
10. Which of the following human genetic disorders is sex linked?
a. hemophilia
Correct. Hemophilia is inherited as an X-linked recessive.
b. PKU
c. cystic fibrosis
d. achondroplasia
e. Tay-Sachs
11. A genetic defect in humans results in the absence of sweat glands in the skin. Some
men have this defect all over their bodies, but in women it is usually expressed in a
peculiar way. A woman with this defect typically has small patches of skin with sweat
glands and other patches where sweat glands are lacking. This pattern suggests the
phenotypic effect of
a. a mutation.
b. chromosome inactivation.
Correct. This pattern suggests that a gene on the X chromosome is involved in the
production of sweat glands. If a female has one X chromosome that directs sweat-gland
production and one that does not, then in those patches where the female lacks sweat
glands the X chromosome carrying the normal sweat-gland allele has been inactivated
and is present as a Barr body.
c. RNA splicing.
d. an operon.
e. a homeobox.
12. Which of the following is correct with regard to aneuploidy?
a. inversion
b. 2n + 1
Correct. An aneuploid individual either has one too many or one too few chromosomes.
c. All aneuploid individuals die before birth.
d. 4n
e. It only involves the autosomes.
13. If a fragment of a chromosome breaks off and then reattaches to the original
chromosome at the same place but in the reverse direction, the resulting chromosomal
abnormality is called
a. a deletion.
b. an inversion.
Correct. The question describes an inversion.
c. a translocation.
d. a nondisjunction.
e. polyploidy.
14. Why are individuals with an extra chromosome 21, which causes Down syndrome,
more numerous than individuals with an extra chromosome 3 or chromosome 16?
a. There are probably more genes on chromosome 21 than on the others.
b. Chromosome 21 is a sex chromosome and 3 and 16 are not.
c. Down syndrome is not more common, just more serious.
d. Extra copies of the other chromosomes are probably fatal.
Correct. Several trisomies have lethal effects.
e. Nondisjunction of chromosomes 3 and 16 probably occurs more frequently.
15. Humans have 23 pairs of chromosomes, while our closest relatives, chimpanzees,
have 24. Chromosome studies indicate that at some point early in human evolution, two
chromosomes simultaneously broke into a large portion and a small portion. The large
parts combined to form a large chromosome, and the small parts combined to form a
much smaller chromosome, which was subsequently lost. This important chromosomal
change could best be described as
a. nondisjunction followed by deletion.
b. translocation followed by deletion.
Correct. The joining of fragments from nonhomologous chromosomes (translocation)
was followed by chromosomal loss (deletion).
c. duplication followed by deletion.
d. translocation followed by inversion.
e. nondisjunction followed by inversion.
16. Each cell in an individual with Down syndrome contains ____ chromosomes.
a. 3
b. 22
c. 24
d. 45
e. 47
Correct. Down syndrome is the result of having three copies of chromosome 21.
17. Disorders involving unusual numbers of sex chromosomes show that maleness in
humans is caused by the
a. presence of an X chromosome.
b. presence of a Y chromosome.
Correct. Regardless of the number of X chromosomes present, an individual with a
normal Y chromosome will have male sex organs.
c. absence of an X chromosome.
d. absence of a Y chromosome.
e. absence of an X chromosome and presence of a Y chromosome.
18. A particular allele can have different effects if it was inherited from a male rather
than a female. This phenomenon is known as
a. extranuclear inheritance.
b. aneuploidy.
c. sex-linkage.
d. Prader-Willi syndrome.
e. genomic imprinting.
Correct. The sex of the bearer of a chromosome can have an effect on that chromosome's
expression in the offspring.
19. Human mitochondria
a. are inherited as an X-linked trait.
b. are all inherited from the father.
c. have linear DNA.
d. do not contain DNA.
e. are all inherited from the mother.
Correct. An individual's mitochondria are all derived from those found in the ovum.
20. Both chloroplasts and mitochondria
a. are found within the nucleus.
b. have linear DNA.
c. carry extranuclear genes.
Correct. Both chloroplasts and mitochondria carry genes.
d. are inherited from both parents.
e. display a Mendelian pattern of inheritance.