Chapter 12 Review
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. The X and Y chromosomes are called the
a. extra chromosomes.
b. phenotypes.
c. sex chromosomes.
d. All of the above
____
2. Down syndrome : nondisjunction ::
a. chromatids : centromere
b. male : XY chromosomes
c. haploid : mitosis
d. meiosis : diploid
____
3. female : XX ::
a. female : gametes
b. female : eggs
c. male : YY
d. male : XY
____
4. Which of the following is the best explanation for the observation that females rarely get the disease
hemophilia?
a. Large quantities of male hormones are necessary in order for the allele carrying the
disease to be expressed.
b. Female fetuses that carry the allele for the disease die before birth.
c. A female could get the disease only by having a mother who is a carrier and a father who
has the disease. Since most males with the disease do not survive to reproductive age, this
is an extremely unlikely event.
d. A female could get the disease only by having parents who are both carriers of the disease.
Because females cannot be carriers, this is an impossible event.
____
5. In a mating between two parental types, one of which is homozygous dominant for two linked traits and one
of which is homozygous recessive for the same two linked traits, evidence of crossing-over would be apparent
in which of the following generations?
a. parents
c. F2
b. F1
d. All of the above
____
6. Which of the following is not true of chromosome maps?
a. They depict the linear sequence of genes on a chromosome.
b. They are constructed using crossing-over data from mating experiments.
c. They depict absolute distances between genes on a chromosome.
d. They are practical with species having only a few chromosomes.
____
7. A mutation caused by a piece of DNA breaking away from its chromosome and becoming attached to a
nonhomologous chromosome is called
a. deletion.
c. inversion.
b. duplication.
d. translocation.
____
8. A change in a gene due to damage or incorrect copying is called
a. evolution.
c. segregation.
b. meiosis.
d. a mutation.
____
9. The effects of a mutation can be
a. helpful.
b. harmful.
c. neutral.
d. All of the above
____ 10. A diagram in which several generations of a family and the occurrence of certain genetic characteristics are
shown is called a
a. Punnett square.
c. pedigree.
b. monohybrid cross.
d. family karyotype.
____ 11. A family record that indicates the occurrence of a trait is a
a. sonogram.
c. pedigree.
b. karyotype.
d. chromosome map.
____ 12. Which of the following traits is controlled by multiple alleles in humans?
a. sickle cell anemia
c. hemophilia
b. blood type
d. pattern baldness
____ 13. What would be the blood type of a person who inherited an A allele from one parent and an O allele from the
other?
a. type A
c. type AB
b. type B
d. type O
____ 14. In humans, the risks of passing on a genetic disorder to one’s children can be assessed by
a. analysis of a pedigree.
b. genetic counseling.
c. prenatal testing.
d. All of the above
____ 15. Genetic counseling is a process that
a. helps identify parents at risk for having children with genetic defects.
b. assists parents in deciding whether or not to have children.
c. uses a family pedigree.
d. All of the above
____ 16. While studying several generations of a particular family, a geneticist observed that a certain disease was
found equally in males and females and that all children who had the disease had parents who also had the
disease. The gene coding for this disease is probably
a. sex-linked recessive.
b. sex-linked dominant.
c. autosomal recessive.
d. autosomal dominant.
____ 17. If both parents carry the recessive allele that causes cystic fibrosis, the chance that their child will develop the
disease is
a. one in two.
c. two in five.
b. one in four.
d. 100%.
____ 18. If a characteristic is sex-linked, it
a. occurs most commonly in males.
b. occurs only in females.
c. can never occur in females.
d. is always fatal.
____ 19. Since the allele for colorblindness is located on the X chromosome, colorblindness
a. cannot be inherited.
b. occurs only in adults.
c. is sex-linked.
d. None of the above
____ 20. People with Down syndrome have
a. 45 chromosomes.
b. 46 chromosomes.
c. 47 chromosomes.
d. no X chromosomes.
____ 21. The sex of an offspring is determined by
a. the mother.
b. the father.
c. both parents.
d. the offspring.
____ 22. If nondisjunction occurs,
a. there will be too many gametes produced.
b. no gametes will be produced.
c. a gamete will receive too many or too few copies of a chromosome.
d. mitosis cannot take place.
____ 23. Consider a cross between a homozygous white-eyed female Drosophila and a red-eyed male Drosophila.
What proportion of the female offspring would be expected to be white-eyed? What proportion of the male
offspring would be expected to be white-eyed?
a. none; all
c. all; none
b. 50%; 50%
d. none; 25%
Completion
Complete each statement.
24. The X and Y chromosomes are called the ____________________ chromosomes.
25. In humans, the genotype XX results in a(n) ____________________.
26. Linked genes can be separated from each other in meiosis if ____________________ occurs.
27. When traits do not appear according to the expected ratio in offspring, ____________________ may have
occurred.
28. When a piece of chromosome attaches itself to a nonhomologous chromosome, the resulting mutation is
called a(n) ____________________.
29. A mutation in which remaining codons are grouped incorrectly is called a(n) ____________________
mutation.
30. A(n) ____________________ trait is one in which males and females can show different phenotypes even
when they have the same genotype.
31. Spontaneous changes in genetic material are called ____________________.
32. Identifying patterns of inheritance within a family over several generations is possible by studying a diagram
called a(n) ____________________.
33. ____________________, in which a defective gene is replaced with a healthy gene, is a treatment being
developed for genetic disorders.
34. A person who is heterozygous for a recessive disorder is called a(n) ____________________.
35. By studying a(n) ____________________, genetic counselors can study how a trait was inherited over
several generations.
36. A genetic disorder resulting in defective blood clotting is ____________________.
37. Phenylkenonuria (PKU) is a genetic disease in which an individual lacks a(n) ____________________
responsible for converting the amino acid phenylalanine into the amino acid tyrosine.
38. A trait that is determined by a gene found only on the X chromosome is said to be ____________________.
39. In humans, the genetic disorder caused by an extra chromosome 21 is called ____________________.
40. The failure of replicated chromosomes to separate is called ____________________.
The partially completed pedigree below is for a family with a genetic disorder.
41. Refer to the illustration above. The father listed in the pedigree is most likely ____________________ for the
trait.
42. Refer to the illustration above. Child 3 probably has a(n) _________________________ phenotype.
Problem
43. In humans, cystic fibrosis is caused by a recessive gene that is not sex-linked. A man and a woman, neither of
whom has cystic fibrosis, have two children with the disease. What is the probability that their third child will
have the disease? Write your answer in the space below.
Essay
44. Explain the mechanism of sex determination in humans. Write your answer in the space below.
45. Explain why crossing-over is an important source of genetic variation. Write your answer in the space below.
46. Discuss the inheritance pattern that would be seen in a pedigree designed to study a recessive sex-linked trait.
Write your answer in the space below.
47. What are the possible genotypes of children born to a man who has the genotype IAi for blood type and a
woman who has the genotype IAIB? What are the possible phenotypes? Write your answer in the space below.
48. In humans, colorblindness is a recessive, sex-linked trait. What is the probability that the children of a woman
heterozygous for colorblindness and a man with normal color vision will be colorblind? Explain your answer.
Write your answer in the space below.
49. Discuss how a karyotype can be used to diagnose Down syndrome. Write your answer in the space below.
Chapter 12 Review
Answer Section
MULTIPLE CHOICE
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C
B
D
C
C
C
D
D
D
C
C
B
A
D
D
D
B
A
C
C
B
C
A
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1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
DIF:
DIF:
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1
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2
1
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1
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1
2
1
1
2
2
1
1
1
1
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3
COMPLETION
24. ANS: sex
PTS: 1
25. ANS: female
DIF: 1
OBJ: 12-1.1
PTS: 1
DIF: 1
26. ANS: crossing-over
OBJ: 12-1.2
PTS: 1
DIF: 1
27. ANS: crossing-over
OBJ: 12-1.4
PTS: 1
DIF: 2
28. ANS: translocation
OBJ: 12-1.4
PTS: 1
DIF: 1
OBJ: 12-1.5
OBJ:
OBJ:
OBJ:
OBJ:
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OBJ:
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OBJ:
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OBJ:
OBJ:
OBJ:
12-1.1
12-1.5
12-1.1
12-1.3
12-1.4
12-1.4
12-1.5
12-1.5
12-1.5
12-2.1
12-2.1
12-2.3
12-2.3
12-2.5
12-2.5
12-2.2
12-2.2
12-1.3
12-1.3
12-1.5
12-1.2
12-1.5
12-1.3
29. ANS: frameshift
PTS: 1
DIF: 1
30. ANS: sex-influenced
OBJ: 12-1.5
PTS: 1
31. ANS: mutations
DIF: 1
OBJ: 12-2.4
PTS: 1
32. ANS: pedigree
DIF: 1
OBJ: 12-1.5
PTS: 1
DIF: 1
33. ANS: Gene therapy
OBJ: 12-2.1
PTS: 1
34. ANS: carrier
DIF: 1
OBJ: 12-2.5
PTS: 1
35. ANS: pedigree
DIF: 1
OBJ: 12-2.2
PTS: 1
36. ANS: hemophilia
DIF: 1
OBJ: 12-2.1
PTS: 1
37. ANS: enzyme
DIF: 1
OBJ: 12-2.2
PTS: 1
38. ANS: sex-linked
DIF: 1
OBJ: 12-2.2
PTS: 1
DIF: 1
39. ANS: Down syndrome
OBJ: 12-2.4
PTS: 1
DIF: 1
40. ANS: nondisjunction
OBJ: 12-1.5
PTS: 1
DIF: 1
41. ANS: heterozygous
OBJ: 12-1.5
PTS: 1
DIF: 2
42. ANS: homozygous recessive
OBJ: 12-2.1
PTS: 1
DIF: 2
OBJ: 12-2.1
PROBLEM
43. ANS:
The probability is 25%. (The probability that any one child will have the disease is 25%. This probability is
entirely independent of the number of children already born with the disease.)
PTS: 1
DIF: 2
OBJ: 12-2.2
ESSAY
44. ANS:
Homologous chromosomes segregate during meiosis I. The sex chromosomes pair and segregate in the same
manner as other chromosomes. Each egg receives one X chromosome. Each sperm receives either an X or a Y
chromosome. If an egg is fertilized by a sperm containing an X chromosome, the resulting zygote will be XX,
and the new individual will be female. If an egg is fertilized by a sperm containing a Y chromosome, the
resulting zygote will be XY, and the new individual will be male.
PTS: 1
DIF: 2
OBJ: 12-1.2
45. ANS:
Crossing-over occurs when two homologous chromosomes exchange reciprocal segments of DNA during
prophase I of meiosis. This results in chromosomes in which allele combinations have been rearranged. When
meiosis is completed, the resulting gametes carry new combinations of genes.
PTS: 1
DIF: 2
OBJ: 12-1.4
46. ANS:
Sex-linked traits are carried on the X chromosome. As a result, recessive sex-linked traits are rarely seen in a
female, unless she is the offspring of an affected male and a female who either is a carrier or is affected.
Males born to a female who is either a carrier or affected may inherit the sex-linked allele. If the female is
affected, both of her X chromosomes will carry the allele under study and all male offspring will inherit it. If
she is a carrier, only one of her X chromosomes will carry the sex-linked allele and male offspring will have a
50-50 chance of inheriting this allele. Because males have only one X chromosome, they do not have a
dominant allele to counteract the effect of the recessive sex-linked allele.
PTS: 1
DIF: 2
OBJ: 12-2.1
47. ANS:
The trait of blood type in humans is determined by multiple alleles. A Punnett square may be used to
determine that the possible genotypes are IAIA, IAIB, IAi, and IBi. The phenotypes that correspond to these
genotypes are blood types A, AB, A, and B, respectively.
PTS: 1
DIF: 2
OBJ: 12-2.3
48. ANS:
Since all the female offspring receive the normal allele for vision from the father, all female offspring will
have normal color vision, although half of them will receive the recessive allele from the mother and thus be
carriers. Since all of the male offspring receive the Y chromosome from the father, it is the X chromosome
they receive from the mother that will determine whether or not they are colorblind. Since the mother is
heterozygous, male offspring will have a 50% chance of being colorblind.
PTS: 1
DIF: 2
OBJ: 12-2.4
49. ANS:
A karyotype is a photograph that shows the collection of chromosomes found in an individual’s cells.
Analysis of this collection of chromosomes can reveal abnormalities in chromosome number. Down
syndrome is associated with an extra chromosome 21 in the cells of a person. Such an abnormality can be
detected by observing a person’s karyotype.
PTS: 1
DIF: 2
OBJ: 12-2.5