1) When Thomas Hunt Morgan crossed his red-eyed F₁
generation flies to each other, the F₂ generation included both red- and
white-eyed flies. Remarkably, all the white-eyed flies were male. What was the
explanation for this result?
A) The gene involved is on the Y chromosome.
B) The gene involved is on the X chromosome.
C) The gene involved is on an autosome, but only in
males.
D) Other male-specific factors influence eye color in
flies.
E) Other female-specific factors influence eye color in
flies.
Answer: B
2) Sturtevant provided genetic evidence for the existence
of four pairs of chromosomes in Drosophila in which of these ways?
A) There are four major functional classes of genes in
Drosophila.
B) Drosophila genes cluster into four distinct groups of
linked genes.
C) The overall number of genes in Drosophila is a
multiple of four.
D) The entire Drosophila genome has approximately 400 map
units.
E) Drosophila genes have, on average, four different
alleles.
Answer: B
3) Which of the following is the meaning of the
chromosome theory of inheritance as expressed in the early 20th century?
A) Individuals inherit particular chromosomes attached to
genes.
B) Mendelian genes are at specific loci on the chromosome
and in turn segregate during meiosis.
C) Homologous chromosomes give rise to some genes and
crossover chromosomes to other genes.
D) No more than a single pair of chromosomes can be found
in a healthy normal cell.
E) Natural selection acts on certain chromosome arrays
rather than on genes.
Answer: B
4) Thomas Hunt Morgan's choice of Drosophila melanogaster
has been proven to be useful even today. Which of the following has/have
continued to make it a most useful species?
I. its four pairs of chromosomes
II. a very large number of visible as well as
biochemically mutant phenotypes
III. easy and inexpensive maintenance
IV. short generation time and large number of offspring
A) I and IV only
B) II and III only
C) I, II, and III only
D) II, III, and IV only
E) I, II, III, IV, and V
Answer: E
5) A woman is found to have 47 chromosomes, including
three X chromosomes. Which of the following describes her expected phenotype?
A) masculine characteristics such as facial hair
B) enlarged genital structures
C) excessive emotional instability
D) normal female
E) sterile female
Answer: D
6) Males are more often affected by sex-linked traits
than females because
A) male hormones such as testosterone often alter the
effects of mutations on the X chromosome.
B) female hormones such as estrogen often compensate for
the effects of mutations on the X chromosome.
C) X chromosomes in males generally have more mutations
than X chromosomes in females.
D) males are hemizygous for the X chromosome.
E) mutations on the Y chromosome often worsen the effects
of X-linked mutations.
Answer: D
7) SRY is best described in which of the following ways?
A) a gene present on the X chromosome that triggers
female development
B) an autosomal gene that is required for the expression
of genes on the Y chromosome
C) a gene region present on the Y chromosome that
triggers male development
D) an autosomal gene that is required for the expression
of genes on the X chromosome
E) a gene required for development, and males or females
lacking the gene do not survive past early childhood
Answer: C
8) In cats, black fur color is caused by an X-linked
allele; the other allele at this locus causes orange color. The heterozygote is
tortoiseshell. What kinds of offspring would you expect from the cross of a
black female and an orange male?
A) tortoiseshell females; tortoiseshell males
B) black females; orange males
C) orange females; orange males
D) tortoiseshell females; black males
E) orange females; black males
Answer: D
9) Red-green color blindness is a sex-linked recessive
trait in humans. Two people with normal color vision have a color-blind son.
What are the genotypes of the parents?
A) XcXc and XcY
B) XcXc and XCY
C) XCXC and XcY
D) XCXC and XCY
E) XCXc and XCY
Answer: E
10) Cinnabar eyes is a sex-linked recessive
characteristic in fruit flies. If a female having cinnabar eyes is crossed with
a wild-type male, what percentage of the F₁ males will have cinnabar eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Answer: E
11) Calico cats are female because
A) the males die during embryonic development.
B) a male inherits only one of the two X-linked genes
controlling hair color.
C) the Y chromosome has a gene blocking orange
coloration.
D) only females can have Barr bodies.
E) multiple crossovers on the Y chromosome prevent orange
pigment production.
Answer: B
12) In birds, sex is determined by a ZW chromosome
scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes
death of the embryo is sometimes present on the Z chromosome in pigeons. What
would be the sex ratio in the offspring of a cross between a male that is
heterozygous for the lethal allele and a normal female?
A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 4:3 male to female
E) 3:1 male to female
Answer: A
13) Sex determination in mammals is due to the SRY region
of the Y chromosome. An abnormality of this region could allow which of the
following to have a male phenotype?
A) Turner syndrome, 45, X
B) translocation of SRY to an autosome of a 46, XX
individual
C) a person with an extra X chromosome
D) a person with one normal and one shortened (deleted) X
E) Down syndrome, 46, XX
Answer: B
14) In humans, clear gender differentiation occurs, not
at fertilization, but after the second month of gestation. What is the first
event of this differentiation?
A) formation of testosterone in male embryos
B) formation of estrogens in female embryos
C) anatomical differentiation of a penis in male embryos
D) activation of SRY in male embryos and masculinization
of the gonads
E) activation of SRY in females and feminization of the
gonads
Answer: D
15) Duchenne muscular dystrophy (DMD) is caused by a gene
on the human X chromosome. The patients have muscles that weaken over time
because they have absent or decreased dystrophin, a muscle protein. They rarely
live past their 20s. How likely is it for a woman to have this condition?
A) Women can never have this condition.
B) One-half of the daughters of an affected man could
have this condition.
C) One-fourth of the children of an affected father and a
carrier mother could have this condition.
D) Very rarely would a woman have this condition; the
condition would be due to a chromosome error.
E) Only if a woman is XXX could she have this condition.
Answer: D
16) Women (and all female mammals) have one active X
chromosome per cell instead of two. What causes this?
A) modification of the XIST gene so that it is active
only on one X chromosome, which then becomes inactive
B) activation of the Barr gene on one of the two X
chromosomes that then inactivates
C) crossover between the XIST gene on one X chromosome
and a related gene on an autosome
D) inactivation of the XIST gene on the X chromosome
derived from the male parent
E) the removal of methyl (CH3) groups from the X
chromosome that will remain active
Answer: A
17) Which of the following statements is true of linkage?
A) The closer two genes are on a chromosome, the lower
the probability that a crossover will occur between them.
B) The observed frequency of recombination of two genes
that are far apart from each other has a maximum value of 100%.
C) All of the traits that Mendel studied–seed color, pod
shape, flower color, and others–are due to genes linked on the same chromosome.
D) Linked genes are found on different chromosomes.
E) Crossing over occurs during prophase II of meiosis.
Answer: A
18) How would one explain a testcross involving F₁
dihybrid flies in which more parental-type offspring than recombinant-type
offspring are produced?
A) The two genes are closely linked on the same
chromosome.
B) The two genes are linked but on different chromosomes.
C) Recombination did not occur in the cell during
meiosis.
D) The testcross was improperly performed.
E) Both of the characters are controlled by more than one
gene.
Answer: A
19) What does a frequency of recombination of 50%
indicate?
A) The two genes are likely to be located on different
chromosomes.
B) All of the offspring have combinations of traits that
match one of the two parents.
C) The genes are located on sex chromosomes.
D) Abnormal meiosis has occurred.
E) Independent assortment is hindered.
Answer: A
20) What is the reason that linked genes are inherited
together?
A) They are located close together on the same
chromosome.
B) The number of genes in a cell is greater than the
number of chromosomes.
C) Chromosomes are unbreakable.
D) Alleles are paired together during meiosis.
E) Genes align that way during metaphase I of meiosis.
Answer: A
21) Three genes at three loci are being mapped in a
particular species. Each has two phenotypes, one of which is markedly different
from the wild type. The unusual allele of the first gene is inherited with
either of the others about 50% of the time. However, the unusual alleles of the
other two genes are inherited together 14.4% of the time. Which of the
following describes what is happening?
A) The genes are showing independent assortment.
B) The three genes are linked.
C) The first gene is linked but the other two are not.
D) The first gene is assorting independently from the
other two that are linked.
E) The first gene is located 14.4 units apart from the
other two.
Answer: D
22) The centimorgan (cM) is a unit named in honor of
Thomas Hunt Morgan. To what is it equal?
A) the physical distance between two linked genes
B) 1% frequency of recombination between two genes
C) 1 nanometer of distance between two genes
D) the distance between a pair of homologous chromosomes
E) the recombination frequency between two genes assorting
independently
Answer: B
23) Recombination between linked genes comes about for
what reason?
A) Mutation on one homolog is different from that on the
other homolog.
B) Independent assortment sometimes fails because Mendel
had not calculated appropriately.
C) When genes are linked they always "travel"
together at anaphase.
D) Crossovers between these genes result in chromosomal
exchange.
E) Nonrecombinant chromosomes break and then re-join with
one another.
Answer: D
24) Why does recombination between linked genes continue
to occur?
A) Recombination is a requirement for independent
assortment.
B) Recombination must occur or genes will not assort
independently.
C) New allele combinations are acted upon by natural
selection.
D) The forces on the cell during meiosis II always result
in recombination.
E) Without recombination there would be an insufficient
number of gametes.
Answer: C
25) Map units on a linkage map cannot be relied upon to
calculate physical distances on a chromosome for which of the following
reasons?
A) The frequency of crossing over varies along the length
of the chromosome.
B) The relationship between recombination frequency and
map units is different in every individual.
C) Physical distances between genes change during the
course of the cell cycle.
D) The gene order on the chromosomes is slightly
different in every individual.
E) Linkage map distances are identical between males and
females.
Answer: A
26) Which of the following two genes are closest on a
genetic map of Drosophila?
A) b and vg
B) vg and cn
C) rb and cn
D) cn and b
E) b and rb
Answer: E
27) If nondisjunction occurs in meiosis II during
gametogenesis, what will be the result at the completion of meiosis?
A) All the gametes will be diploid.
B) Half of the gametes will be n + 1, and half will be n
- 1.
C) 1/4 of the gametes will be n + 1, 1/4 will be n - 1,
and 1/2 will be n.
D) There will be three extra gametes.
E) Two of the four gametes will be haploid, and two will
be diploid.
Answer: C
28) One possible result of chromosomal breakage is for a
fragment to join a nonhomologous chromosome. What is this alteration called?
A) deletion
B) transversion
C) inversion
D) translocation
E) duplication
Answer: D
29) A nonreciprocal crossover causes which of the
following products?
A) deletion only
B) duplication only
C) nondisjunction
D) deletion and duplication
E) duplication and nondisjunction
Answer: D
30) In humans, male-pattern baldness is controlled by an
autosomal gene that occurs in two allelic forms. Allele Hn determines
nonbaldness, and allele Hb determines pattern baldness. In males, because of
the presence of testosterone, allele Hb is dominant over Hn. If a man and woman
both with genotype HnHb have a son, what is the chance that he will eventually
be bald?
A) 0%
B) 25%
C) 33%
D) 50%
E) 75%
Answer: E
31) Of the following human aneuploidies, which is the one
that generally has the most severe impact on the health of the individual?
A) 47, +21
B) 47, XXY
C) 47, XXX
D) 47, XYY
E) 45, X
Answer: A
32) A phenotypically normal prospective couple seeks
genetic counseling because the man knows that he has a translocation of a
portion of his chromosome 4 that has been exchanged with a portion of his
chromosome 12. Although he is normal because his translocation is balanced, he
and his wife want to know the probability that his sperm will be abnormal. What
is your prognosis regarding his sperm?
A) 1/4 will be normal, 1/4 will have the translocation,
and 1/2 will have duplications and deletions.
B) All will carry the same translocation as the father.
C) None will carry the translocation since abnormal sperm
will die.
D) His sperm will be sterile and the couple might
consider adoption.
E) 1/2 will be normal and the rest will have the father's
translocation.
Answer: A
33) Abnormal chromosomes are frequently found in
malignant tumors. Errors such as translocations may place a gene in close
proximity to different control regions. Which of the following might then occur
to make the cancer worse?
A) an increase in nondisjunction
B) expression of inappropriate gene products
C) a decrease in mitotic frequency
D) death of the cancer cells in the tumor
E) sensitivity of the immune system
Answer: B
34) An inversion in a human chromosome often results in
no demonstrable phenotypic effect in the individual. What else may occur?
A) There may be deletions later in life.
B) Some abnormal gametes may be formed.
C) There is an increased frequency of mutation.
D) All inverted chromosomes are deleted.
E) The individual is more likely to get cancer.
Answer: B
35) What is the source of the extra chromosome 21 in an individual
with Down syndrome?
A) nondisjunction in the mother only
B) nondisjunction in the father only
C) duplication of the chromosome
D) nondisjunction or translocation in either parent
E) It is impossible to detect with current technology.
Answer: D
36) Down syndrome has a frequency in the U.S. population
of ~1/700 live births. In which of the following groups would you expect this
frequency to be significantly higher?
A) people in Latin or South America
B) the Inuit and other peoples in very cold habitats
C) people living in equatorial areas of the world
D) very small population groups
E) No groups have such higher frequency.
Answer: E
37) A couple has a child with Down syndrome. The mother
is 39 years old at the time of delivery. Which of the following is the most
probable cause of the child's condition?
A) The woman inherited this tendency from her parents.
B) One member of the couple carried a translocation.
C) One member of the couple underwent nondisjunction in
somatic cell production.
D) One member of the couple underwent nondisjunction in
gamete production.
E) The mother had a chromosomal duplication.
Answer: D
38) In 1956 Tijo and Levan first successfully counted
human chromosomes. What is the reason it took so many years to do so?
A) Watson and Crick's structure of DNA was not done until
1953.
B) Chromosomes were piled up on top of one another in the
nucleus.
C) Chromosomes were not distinguishable during
interphase.
D) A method had not yet been devised to halt mitosis at
metaphase.
E) Chromosomes were piled up on top of one another in the
nucleus, chromosomes were not distinguishable during interphase, and a method
had not yet been devised to halt mitosis at metaphase.
Answer: E
39) At which phase(s) is it preferable to obtain
chromosomes to prepare a karyotype?
A) early prophase
B) late telophase
C) anaphase
D) late anaphase or early telophase
E) late prophase or metaphase
Answer: E
40) What is a syndrome?
A) a characteristic facial appearance
B) a group of traits, all of which must be present if an
aneuploidy is to be diagnosed
C) a group of traits typically found in conjunction with
a particular chromosomal aberration or gene mutation
D) a characteristic trait usually given the discoverer's
name
E) a characteristic that only appears in conjunction with
one specific aneuploidy
Answer: C
41) Which of the following is known as a Philadelphia
chromosome?
A) a human chromosome 22 that has had a specific
translocation
B) a human chromosome 9 that is found only in one type of
cancer
C) an animal chromosome found primarily in the
mid-Atlantic area of the United States
D) an imprinted chromosome that always comes from the
mother
E) a chromosome found not in the nucleus but in
mitochondria
Answer: A
42) At what point in cell division is a chromosome lost
so that, after fertilization with a normal gamete, the result is an embryo with
45, X?
I. an error in anaphase I
II. an error in anaphase II
III. an error of the first postfertilization mitosis
IV. an error in pairing
A) I or II only
B) II or IV only
C) III or IV only
D) I, II, or III only
E) I, II, III, or IV
Answer: E
43) Which of the following is true of aneuploidies in
general?
A) A monosomy is more frequent than a trisomy.
B) 45 X is the only known human live-born monosomy.
C) Some human aneuploidies have selective advantage in
some environments.
D) Of all human aneuploidies, only Down syndrome is
associated with mental retardation.
E) An aneuploidy resulting in the deletion of a
chromosome segment is less serious than a duplication.
Answer: B
44) A gene is considered to be non-Mendelian in its
inheritance pattern if it seems to "violate" Mendel's laws. Which of
the following would be considered Mendelian?
A) a gene whose expression varies depending on the gender
of the transmitting parent
B) a gene derived solely from maternal inheritance
C) a gene transmitted via the cytoplasm or cytoplasmic
structures
D) a gene transmitted to males from the maternal line and
from fathers to daughters
E) a gene transmitted by a virus to egg-producing cells
Answer: D
45) Genomic imprinting is generally due to the addition
of methyl (–CH3) groups to C nucleotides in order to silence a given gene. If
this depends on the sex of the parent who transmits the gene, which of the
following must be true?
A) Methylation of C is permanent in a gene.
B) Genes required for early development stages must not
be imprinted.
C) Methylation of this kind must occur more in males than
in females.
D) Methylation must be reversible in ovarian and
testicular cells.
E) The imprints are transmitted only to gamete-producing
cells.
Answer: D
46) Correns described that the inheritance of variegated
color on the leaves of certain plants was determined by the maternal parent
only. What phenomenon does this describe?
A) mitochondrial inheritance
B) chloroplast inheritance
C) genomic imprinting
D) infectious inheritance
E) sex-linkage
Answer: B
47) Mitochondrial DNA is primarily involved in coding for
proteins needed for electron transport. Therefore, in which body systems would
you expect most mitochondrial gene mutations to be exhibited?
A) the immune system and the blood
B) the excretory and respiratory systems
C) the skin and senses
D) the nervous and muscular systems
E) the circulation system
Answer: D
48) A certain kind of snail can have a right-handed
direction of shell coiling (D) or left-handed coiling (d). If direction of
coiling is due to a protein deposited by the mother in the egg cytoplasm, then
a Dd egg-producing snail and a dd sperm-producing snail will have offspring of
which genotype(s) and phenotype(s)?
A) 1/2 Dd:1/2 dd; all right coiling
B) all Dd; all right coiling
C) 1/2 Dd:1/2 dd; half right and half left coiling
D) all Dd; all left coiling
E) all Dd; half right and half left coiling
Answer: A
49) Which of the following produces a Mendelian pattern of
inheritance?
A) genomic imprinting
B) a mitochondrial gene mutation
C) a chloroplast gene mutation
D) viral genomes that inhabit egg cytoplasm
E) a trait acted upon by many genes
Answer: E
50) Suppose that a gene on human chromosome 18 can be
imprinted in a given pattern in a female parent but not in a male parent. A
couple in whom each maternal meiosis is followed by imprinting of this gene
have children. What can we expect as a likely outcome?
A) All sons but no daughters will bear their mother's
imprinting pattern.
B) All daughters but no sons will bear their mother's
imprinting pattern.
C) All sons and daughters will have a 50% chance of
receiving the mother's imprinting pattern.
D) All the children will bear their mother's imprinting
pattern but only daughters will then pass it down.
E) Each of the children will imprint a different
chromosome.
Answer: D
51. This a map of four genes on a chromosome (See Image)
Between which two genes would you expect the highest
frequency of recombination?
A) A and W
B) W and E
C) E and G
D) A and E
E) A and G
Answer: E
52) In a series of mapping experiments, the recombination
frequencies for four different linked genes of Drosophila were determined as
shown in Figure
What is the order of these genes on a chromosome map?
A) rb-cn-vg-b
B) vg-b-rb-cn
C) cn-rb-b-vg
D) b-rb-cn-vg
E) vg-cn-b-rb
Answer: D
53) The pedigree in Figure shows the transmission of
a trait in a particular family.
Based on this pattern of transmission, the
trait is most likely
A) mitochondrial.
B) autosomal recessive.
C) sex-linked dominant.
D) sex-linked recessive.
E) autosomal dominant.
Answer: A
54. A man who is an achondroplastic dwarf with normal
vision marries a color-blind woman of normal height. The man's father was 6
feet tall, and both the woman's parents were of average height. Achondroplastic
dwarfism is autosomal dominant, and red-green color blindness is X-linked
recessive.
How many of their daughters might be expected to be
color-blind dwarfs?
A) all
B) none
C) half
D) one out of four
E) three out of four
Answer: B
55. A man who is an achondroplastic dwarf with normal
vision marries a color-blind woman of normal height. The man's father was 6
feet tall, and both the woman's parents were of average height. Achondroplastic
dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
What proportion of their sons would be color-blind and of
normal height?
A) none
B) half
C) one out of four
D) three out of four
E) all
Answer: B
56. A man who is an achondroplastic dwarf with normal
vision marries a color-blind woman of normal height. The man's father was 6
feet tall, and both the woman's parents were of average height. Achondroplastic
dwarfism is autosomal dominant, and red-green color blindness is X-linked
recessive.
They have a daughter who is a dwarf with normal color
vision. What is the probability that she is heterozygous for both genes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Answer: E
57. A plantlike organism on the planet Pandora can have
three recessive genetic traits: bluish leaves, due to an allele (a) of gene A;
a feathered stem, due to an allele (b) of gene B; and hollow roots due to an
allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
Which of the following are the phenotypes of the parents
in this cross?
A) 2 and 5
B) 1 and 6
C) 4 and 8
D) 3 and 7
E) 1 and 2
Answer: C
58. A plantlike organism on the planet Pandora can have
three recessive genetic traits: bluish leaves, due to an allele (a) of gene A;
a feathered stem, due to an allele (b) of gene B; and hollow roots due to an
allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had
been found to be heterozygous for the three recessive traits and she was able
to identify progeny of the following phenotypic distribution (+ = wild type):
In which progeny phenotypes has there been recombination
between genes A and B?
A) 1, 2, 5, and 6
B) 1, 3, 6, and 7
C) 2, 4, 5, and 8
D) 2, 3, 5, and 7
E) in all 8 of them
Answer: A
59. A plantlike organism on the planet Pandora can have
three recessive genetic traits: bluish leaves, due to an allele (a) of gene A;
a feathered stem, due to an allele (b) of gene B; and hollow roots due to an
allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had
been found to be heterozygous for the three recessive traits and she was able
to identify progeny of the following phenotypic distribution (+ = wild type):
If recombination is equal to distance in centimorgans
(cM), what is the approximate distance between genes A and B?
A) 1.5 cM
B) 3 cM
C) 6 cM
D) 15 cM
E) 30 cM
Answer: B
60. A plantlike organism on the planet Pandora can have
three recessive genetic traits: bluish leaves, due to an allele (a) of gene A;
a feathered stem, due to an allele (b) of gene B; and hollow roots due to an
allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had
been found to be heterozygous for the three recessive traits and she was able
to identify progeny of the following phenotypic distribution (+ = wild type):
What is the greatest benefit of having used a testcross
for this experiment?
A) The homozygous recessive parents are obvious to the
naked eye.
B) The homozygous parents are the only ones whose
crossovers make a difference.
C) Progeny can be scored by their phenotypes alone.
D) All of the progeny will be heterozygous.
E) The homozygous recessive parents will be unable to
cross over.
Answer: C
61. A plantlike organism on the planet Pandora can have
three recessive genetic traits: bluish leaves, due to an allele (a) of gene A;
a feathered stem, due to an allele (b) of gene B; and hollow roots due to an
allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had
been found to be heterozygous for the three recessive traits and she was able
to identify progeny of the following phenotypic distribution (+ = wild type):
The greatest distance among the three genes is between a
and c. What does this mean?
A) Gene a is closest to b.
B) Genes are in the order: a–b–c.
C) Gene a is not recombining with c.
D) Gene a is between b and c.
E) Distance a–b is equal to distance a–c.
