Chapter 8

Question 1

The centromere is located approximately in the middle of which type of chromosome?

a. Acrocentric
b. Metacentric
c. Paracentric
d. Submetacentric
e. Telocentric

Answer 1

b. Metacentric

Question 2

Which type of chromosome has a centromere displaced toward one end, creating a long arm and a short arm?

a. Acrocentric
b. Metacentric
c. Paracentric
d. Submetacentric
e. Telocentric

Answer 2

d. Submetacentric

Question 3

The centromere is near one end, producing a long arm and a knob, in which type of chromosome?

a. Acrocentric
b. Metacentric
c. Paracentric
d. Submetacentric
e. Telocentric

Answer 3

a. Acrocentric

Question 4

The centromere is at or very near the end in which type of chromosome?

a. Acrocentric
b. Metacentric
c. Paracentric
d. Submetacentric
e. Telocentric

Answer 4

e. Telocentric

Question 5

The complete set of chromosomes possessed by an organism is called a

a. polyploid.
b. chromatin complement.
c. karyotype.
d. genotype.
e. diploid.

Answer 5

c. karyotype.

Question 6

Which type of chromosome mutation increases the amount of genetic material for all chromosomes?

a. Translocation
b. Aneuploidy
c. Polyploidy
d. Inversion
e. Transversion

Answer 6

c. Polyploidy

Question 7

Which type of chromosome mutation decreases the amount of genetic material for one entire chromosome?

a. Translocation
b. Aneuploidy
c. Polyploidy
d. Inversion
e. Transversion

Answer 7

b. Aneuploidy

Question 8

How is colchicine useful for studying chromosomal mutations?

a. Colchicine inhibits microtubule polymerization, which stalls cells in metaphase with condensed chromosomes.
b. Colchicine induces chromosome condensation during interphase, which allows the visualization of interphase chromosomes.
c. Colchicine causes chromosomal breakage, leading to inversions and translocations that can be observed with a microscope.
d. Colchicine aids in the formation of microtubules during mitosis, which promotes anaphase and completion of the cell cycle.
e. Colchicine is an inhibitor of oxidative phosphorylation. Reduced mitochondrial function slows down mitosis and increases the number of metaphase cells.

Answer 8

a. Colchicine inhibits microtubule polymerization, which stalls cells in metaphase with condensed chromosomes.

Question 9

___________ can cause genes to move from one linkage group to another.

a. Inversions
b. Deletions
c. Polyploidy
d. Translocations
e. Unequal crossing over

Answer 9

d. Translocations

Question 10

Which of the following is not a rearrangement that causes chromosomal mutations?

a. Deletion
b. Duplication
c. Inversion
d. Translocation
e. Transversion

Answer 10

e. Transversion

Question 11

Which type of chromosome mutation decreases the amount of genetic material?

a. Deletion
b. Duplication
c. Inversion
d. Translocation
e. Transversion

Answer 11

a. Deletion

Question 12

Which type of chromosome mutation increases the amount of genetic material?

a. Deletion
b. Duplication
c. Inversion
d. Translocation
e. Transversion

Answer 12

b. Duplication

Question 13

Which type of chromosome mutation results in a chromosome segment that is turned 180 degrees?

a. Deletion
b. Duplication
c. Inversion
d. Translocation
e. Transversion

Answer 13

c. Inversion

Question 14

Chimpanzees, gorillas, and orangutans all have 48 chromosomes, whereas humans have 46. Human chromosome 2 is a large, metacentric chromosome with G-banding patterns that closely match those found on two different acrocentric chromosomes of the apes. What would best explain these findings?

a. A translocation took place in a human ancestor, creating a large metacentric chromosome from the two long arms of the ancestral acrocentric chromosomes. The other small chromosome produced by this translocation was lost.
b. Meiotic nondisjunction gave rise to a nullisomic gamete. The fusion of two nullisomic gametes produced the ancestor of the human species with 46 chromosomes instead of 48.
c. A nonreciprocal translocation and subsequent fusion of the chromosomal fragments created a genome of 46 chromosomes without the loss of any genetic information.
d. Infection by a primate virus created a new chromosome when the viral DNA became a permanent part of the genome. Humans were not affected by this virus, so they did not acquire the extra chromosome.
e. Humans have the correct number of chromosomes. The extra chromosome pair in the other apes is a classic case of tetrasomy as a result of meiotic nondisjunction in the primate ancestor.

Answer 14

a. A translocation took place in a human ancestor, creating a large metacentric chromosome from the two long arms of the ancestral acrocentric chromosomes. The other small chromosome produced by this translocation was lost.

Question 15

Approximately ______ of the gametes produced by an individual heterozygous for a translocation will be nonviable.

a. all
b. half
c. none
d. a quarter
an eighth

Answer 15

b. half

Question 16

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P Q R
S T U V • W Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 16

a. Deletion

Question 17

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P O P Q R
S T U V • W X Y Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 17

b. Tandem duplication

Question 18

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P Q R
S T X Y U V • W X Y Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 18

c. Displaced duplication

Question 19

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P R Q Q R
S T U V • W X Y Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 19

d. Reverse duplication

Question 20

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P Q R
S T X W • V U Y Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 20

e. Pericentric inversion

Question 21

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O R Q P
S T U V • W X Y Z

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 21

f. Paracentric inversion

Question 22

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O P Q R Y Z
S T U V • W X

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
Reciprocal translocation

Answer 22

g. Nonreciprocal translocation

Reciprocal translocation

Question 23

Two chromosomes have the following segments, where • represents the centromere:

K L M • N O P Q R
S T U V • W X Y Z

What type of chromosome mutation would result in the following chromosomes:

K L M • N O X Y Z
S T U V • W P Q R

a. Deletion
b. Tandem duplication
c. Displaced duplication
d. Reverse duplication
e. Pericentric inversion
f. Paracentric inversion
g. Nonreciprocal translocation
h. Reciprocal translocation

Answer 23

h. Reciprocal translocation

Question 24

Which of the following is a form of aneuploidy in which two members of the same homologous pair are absent?

a. Nullisomy
b. Monosomy
c. Disomy
d. Trisomy
e. Tetrasomy

Answer 24

a. Nullisomy

Question 25

Which form of aneuploidy describes an organism that is missing a single chromosome?

a. Nullisomy
b. Monosomy
c. Disomy
d. Trisomy
e. Tetrasomy

Answer 25

b. Monosomy

Question 26

Which of the following is not a form of aneuploidy in diploid organisms?

a. Nullisomy
b. Monosomy
c. Disomy
d. Trisomy
e. Tetrasomy

Answer 26

c. Disomy

Question 27

Which form of aneuploidy causes primary Down syndrome?

a. Nullisomy
b. Monosomy
c. Disomy
d. Trisomy
e. Tetrasomy

Answer 27

d. Trisomy

Question 28

Which of the following is a form of aneuploidy in which four members of the same homologous pair are present?

a. Nullisomy
b. Monosomy
c. Disomy
d. Trisomy
e. Tetrasomy

Answer 28

e. Tetrasomy

Question 29

The inheritance of both chromosomes from the same parent is a condition called

a. displaced duplication.
b. uniparental disomy.
c. tandem duplication.
d. unbalanced polymorphism.
e. nondisjunction.

Answer 29

b. uniparental disomy.

Question 30

What is responsible for primary Down syndrome?

a. Disomy
b. Inversion
c. Nondisjunction
d. Polyploidy
e. Translocation

Answer 30

c. Nondisjunction

Question 31

Which type of chromosome mutation is responsible for familial Down syndrome?

a. Disomy
b. Inversion
c. Nondisjunction
d. Polyploidy
e. Translocation

Answer 31

e. Translocation

Question 32

What would be the consequence of a diploid gamete (resulting from meiotic nondisjunction) being fertilized by a haploid gamete from the same species?

a. Allodiploid
b. Allotriploid
c. Autotriploid
d. Allotetraploid
e. Autotetraploid

Answer 32

c. Autotriploid

Question 33

A man has a condition where all of his gametes undergo nondisjunction of the sex chromosomes in meiosis I, but meiosis II proceeds normally. He mates with a woman who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Turner syndrome (XO)? Assume that all gametes and zygotes are viable.

a. 1/8
b. 1/4
c. 1/3
d. 1/2
e. 0

Answer 33

d. 1/2

Question 34

A man has a condition where all of his gametes undergo nondisjunction of the sex chromosomes in meiosis I, but meiosis II proceeds normally. He mates with a woman who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Klinefelter syndrome (XXY)? Assume that all gametes and zygotes are viable.

a. 1/8
b. 1/4
c. 1/3
d. 1/2
e. 0

Answer 34

d. 1/2

Question 35

A man has a condition where all of his gametes undergo meiosis I normally, but there is nondisjunction of the sex chromosomes in every meiosis II. He mates with a woman who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Klinefelter syndrome (XXY)? Assume that all gametes and zygotes are viable.

a. 1/8
b. 1/4
c. 1/3
d. 1/2
e. 0

Answer 35

e. 0

Question 36

A woman has a condition where all of her gametes undergo nondisjunction of chromosome 21 in meiosis I, but meiosis II proceeds normally. She mates with a man who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Down syndrome? Assume that all gametes and zygotes are viable.

a. 1/8
b. 1/4
c. 1/3
d. 1/2
e. 0

Answer 36

d. 1/2

Question 37

A human embryo is produced by the fusion of two gametes that have a normal complement of sex chromosomes. This individual develops into an adult and is diagnosed with Turner syndrome. How can this be?

a. An X chromosome was lost soon after fertilization, leading to mosaic individual with a mixture of XX and XO cells.
b. Nondisjunction produced a gamete that lacked any sex chromosome. This gamete was fertilized, which resulted in the individual with Turner syndrome.
c. This individual is a gynandromorph with a mixture of both male and female characteristics.
d. The embryo was exposed to colchicine soon after fertilization, which produced a polyploidy individual. Dosage compensation caused an imbalance between autosomal and X chromosome gene expression.
e. A nonreciprocal translocation between the X chromosome and an autosome resulted in the loss of one of the X chromosomes.

Answer 37

a. An X chromosome was lost soon after fertilization, leading to mosaic individual with a mixture of XX and XO cells.

Question 38

Wild-type Arabidopsis has 5 chromosomes (2n = 10). Trisomic plants are designated as “Tr” followed by the trisomic chromosome number—that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross wt × Tr1 will have a wild-type chromosomal complement?

a. 1/2
b. 1/3
c. 1/4
d. 1/9
e. 1/81

Answer 38

b. 1/3

Question 39

Wild-type Arabidopsis has 5 chromosomes (2n = 10). Trisomic plants are designated as “Tr” followed by the trisomic chromosome number—that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross Tr1 × Tr1 will have a wild-type chromosomal complement?

a. 1/2
b. 1/3
c. 1/4
d. 1/9
e. 1/81

Answer 39

d. 1/9

Question 40

Wild-type Arabidopsis has 5 chromosomes (2n = 10). Trisomic plants are designated as “Tr” followed by the trisomic chromosome number—that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross wt × Tr1;Tr2 will have a wild-type chromosomal complement?

a. 1/2
b. 1/3
c. 1/4
d. 1/9
e. 1/81

Answer 40

d. 1/9

Question 41

Wild-type Arabidopsis has 5 chromosomes (2n = 10). Trisomic plants are designated as “Tr” followed by the trisomic chromosome number—that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross Tr1;Tr2 × Tr1;Tr2 will have a wild-type chromosomal complement?

a. 1/2
b. 1/3
c. 1/4
d. 1/9
e. 1/81

Answer 41

e. 1/81

Question 42

What type of organism results from the hybridization of a haploid gamete from one species with a diploid gamete from a different species?

a. Allodiploid
b. Allotriploid
c. Autotriploid
d. Allotetraploid
e. Autotetraploid

Answer 42

b. Allotriploid

Question 43

Which type of polyploidy is synonymous with amphidiploid?

a. Allodiploid
b. Allotriploid
c. Autotriploid
d. Allotetraploid
e. Autotetraploid

Answer 43

d. Allotetraploid

Question 44

A plant species has 2n = 18 chromosomes. How many chromosomes would you expect to find in a tetrasomic individual of this species?

a. 17
b. 19
c. 20
d. 22
e. 36

Answer 44

c. 20

Question 45

A newly discovered species of dung beetle has 2n = 16 chromosomes. It mates with a closely related beetle species that has 2n = 12 chromosomes. How many chromosomes would there be in an allotriploid beetle produced from this cross?

a. 13 or 17
b. 19 or 25
c. 18 or 24
d. 20 or 22
e. 36 or 48

Answer 45

d. 20 or 22

Question 46

A newly discovered species of dung beetle has 2n = 16 chromosomes. It mates with a closely related beetle species that has 2n = 12 chromosomes. How many chromosomes would there be in an amphidiploid beetle produced from this cross?

a. 12
b. 14
c. 16
d. 28
e. 12 or 16

Answer 46

d. 28

Question 47

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA) and Musa balbisiana (genome = BB). The Cavendish banana (genome = AAA), the variety most often sold in grocery stores, has what type of genome?

a. Allodiploid
b. Allotriploid
c. Autotriploid
d. Allotetraploid
e. Autotetraploid

Answer 47

c. Autotriploid

Question 48

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA) and Musa balbisiana (genome = BB). Some bananas have genome AAB, which is an example of which kind of polyploidy?

a. Allodiploid
b. Allotriploid
c. Autotriploid
d. Allotetraploid
e. Autotetraploid

Answer 48

b. Allotriploid

Question 49

Arabidopsis thaliana has 2n = 10 chromosomes, and a close relative Capsella rubella has 2n = 16. You have created a hybrid between them and suspect that it is an allotetraploid. If you are right, what possible chromosome numbers could the hybrid have?

a. 20
b. 23
c. 26
d. 29
e. 32
f. All of the above
g. 20 or 32
h. 23 or 26 or 29

Answer 49

h. 23 or 26 or 29

Question 50

List the four basic types of chromosome rearrangements.

Answer 50

Deletions, duplications, inversions, and translocations.

Question 51

Given an individual with a single recessive allele, explain how a deletion could result in the expression of the recessive phenotype.

Answer 51

If a recessive allele for a locus is present on one chromosome, and the homologous chromosome contains a deletion of that locus, then the recessive allele will be expressed, because no wild-type product is produced to mask the recessive phenotype. The normally recessive alleles expressed in individuals heterozygous for deletions are said to display pseudodominance.

Question 52

A female rat that is heterozygous for an autosomal reciprocal translocation has 36 eggs that were generated from the following 9 meioses: 4 by alternate segregation, 4 by adjacent-1 segregation, and 1 by adjacent-2 segregation. She is mated to a chromosomally wild-type male. What is the probability that her offspring will inherit a chromosome bearing the translocation?

Answer 52

Both adjacent-1 and adjacent-2 segregation will produce nonviable offspring because the resulting zygote will have a duplication or deletion of large portions of the reciprocal chromosomes. Therefore, only the offspring derived from gametes of the alternate segregation need be considered. Half of the meiotic products from alternate segregation have translocation chromosomes, so the probability is 50% that the viable offspring will bear these chromosomes.

Question 53

Describe two ways in which an inversion can alter gene expression.

Answer 53

(1) Position effect: Inversions may reposition alleles in different genomic contexts, which may significantly alter their expression. For example, alleles may be repositioned to a heterochromatic region and be inhibited, or to a highly active region and be induced.
(2) Gene disruption: Because inversions involve cutting pieces of chromosomes and splicing pieces of chromosomes back together, gene sequences may be disrupted. Breakpoints can occur in gene regulatory regions, coding domains, introns, and so forth, any or all of which may ultimately alter phenotypic expression.

Question 54

How can a chromosome deletion be detected?

Answer 54

(1) Large deletions can be easily seen by means of microscopy because the chromosome will be shortened. In heterozygotes, this will be obvious because sections of the longer chromosome (corresponding to the region missing in the truncated chromosome) will form unpaired loops of chromatin during meiotic pairing.
(2) If the deletions are relatively small and contain known genetic markers, no recombination will be observed for the markers located within the deleted section.
(3) In deletion heterozygotes, phenotypic expression of recessive alleles, present on the undeleted chromosome, can be expressed. This phenomenon is called pseudodominance.
(4) Deletions can also cause imbalances in the formation of quantifiable gene products (i.e., gene dosage difference). For example, quantification of specific gene products (e.g., levels of protein or mRNA, biochemical assays for production, or activities of specific enzymes) in individuals with different genotypes (e.g., heterozygote versus homozygote) could indicate the number of functional alleles present. Note in this case, however, that the presence of a nonfunctional allele would cause the same phenotype as a deleted allele because in neither case would product be formed.

Question 55

What are three ways that aneuploidy can arise?

Answer 55

(1) Aneuploidy can arise from fertilization between balanced gametes from one parent and unbalanced gametes from the other parent. The unbalanced gametes were formed by chromosome nondisjunction during meiosis.
(2) Aneuploidy can arise from balanced gametes from one parent combining with unbalanced gametes present in individuals that are translocation carriers (e.g., familial Down syndrome). The unbalanced gametes were formed through the anomalous segregation of chromosomes during meiosis.
(3) Aneuploidy can arise from nondisjunction of chromosomes during a mitotic division in autosomal cells. This can create patches of aneuploid cells next to patches of cells with normal chromosome complements, forming mosaics.