Deck 8: Chromosome Variation

Question 1

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 1

D

Question 2

How is colchicine, the chemical used in preparing karyotypes, useful for studying chromosomal mutations?

A) Colchicine prevents cells from entering anaphase, stalling them 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 ruptures the cell membrane, allowing the spreading of cells on microscope slides.
E) Colchicine causes cells to exit the cell cycle, making the chromosome easier to visualize.

Answer 2

A

Question 3

What typically happens to the small fragment generated by a Robertsonian translocation?

A) The small fragment duplicates continuously.
B) The small fragment remains stable.
C) The small fragment often gets lost.
D) The small fragment pairs up with its homologous chromosome.
E) The small fragment tends to recombine back to a larger chromosome.

Answer 3

C

Question 4

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

A) acrocentric
B) metacentric
C) paracentric
D) submetacentric
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.

Question 6

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

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

Question 8

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

A) all
B) half
C) none
D) a quarter
E) an eighth

Question 9

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

A) translocation
B) aneuploidy
C) polyploidy
D) inversion
E) transversion

Question 10

Which of the following chromosome rearrangements represents inversion?

A) A
B) B
C) C
D) D

Question 11

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

A) deletion
B) duplication
C) inversion
D) translocation
E) transversion

Question 12

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

Question 13

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

A) acrocentric
B) metacentric
C) paracentric
D) submetacentric
E) telocentric

Question 14

An individual heterozygous for a reciprocal translocation possesses the following chromosomes:
A B $\bullet$ C DE F G
A B $\bullet$ C DVW X
R S $\bullet$ T UE F G
R S $\bullet$ T UVW X
Will the products from alternate, adjacent-1, or adjacent-2 segregation be missing some genes?

A) alternate segregation
B) adjacent-1 segregation
C) alternate and adjacent-1 segregation
D) alternate and adjacent-2 segregation
E) adjacent-1 and adjacent-2 segregation

Question 15

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

A) deletion
B) duplication
C) inversion
D) translocation
E) All these rearrangements cause chromosomal mutations.

Question 16

Which of the following is represented in the figure?

A) pericentric inversion
B) reciprocal translocation
C) nonreciprocal translocation
D) duplication
E) equal crossing over

Question 17

In order to perform karyotype analysis, chromosomes are obtained from actively dividing cells and treated with chemicals to keep them at the _____ stage of mitosis.

A) prophase
B) interphase
C) anaphase
D) telophase
E) metaphase

Question 18

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. Which statement 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.

Question 19

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

A) deletion
B) duplication
C) inversion
D) translocation
E) transversion

Question 20

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

A) Inversions
B) Deletions
C) Polyploidy
D) Translocations
E) Unequal crossing over

Question 21

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

A) nullisomy
B) monosomy
C) disomy
D) trisomy
E) tetrasomy

Question 22

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

Question 23

Which of the following statements about chromosomal inversions is NOT true?

A) The individual organisms have neither lost nor gained any genetic material.
B) An inversion can break a gene into two parts and separate each to different locations.
C) The expression of the gene may be altered due to the positional effect.
D) The inversion mutations will not likely have pronounced phenotypic effects since there is no loss of genetic material.
E) Individuals heterozygous for inversions may end up producing abnormal gametes.

Question 24

Which of the following statements regarding the Drosophila Bar phenotype is NOT true?

A) Unequal crossing over event may give a rise to the duplication of the Bar region.
B) The trait is inherited as a complete dominant where both homozygous and heterozygous show similar phenotype.
C) The more Bar segment copy the fly has, the more reduced the facets in the eyes get.
D) The Bar phenotype reflects the genetic phenomenon called gene dosage effect.
E) The balance of gene product is critical to cell function and normal development.

Question 25

What is responsible for primary Down syndrome?

A) disomy
B) inversion
C) nondisjunction
D) polyploidy
E) translocation

Question 26

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

Question 27

Which form of aneuploidy causes primary Down syndrome?

A) nullisomy
B) monosomy
C) disomy
D) trisomy
E) tetrasomy

Question 28

Two nonhomologous chromosomes have the following segments:
A • B C D E F G
R • S T U V W X
Draw chromosomes that would result from the following chromosome rearrangements.
a. Reciprocal translocation of CD and TU
b. Reciprocal translocation of CD and W
c. Robertsonian translocation

Question 29

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

Question 30

An individual that is heterozygous for a paracentric inversion has the following chromosomes:
A B • C D E F G H I
A B • C F E D G H I
a. Sketch the pairing of these two chromosomes during prophase I of meiosis, showing all four strands.
b. Draw the chromosomes that would ultimately result from a single crossover between the E and F segments.
c. What will happen when the chromosomes separate in anaphase I of meiosis?

Question 31

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

A) nullisomy
B) monosomy
C) disomy
D) trisomy
E) tetrasomy

Question 32

You are studying the inheritance of the autosomal recessive traits, curly wings (cy) and ebony body color (e), in Drosophila. The cy locus is on chromosome 2 and the e locus is on chromosome 3. In the course of this study, you identify a strain of flies that carries a translocation between chromosome 2 and chromosome 3. Neither cy nor e is located in the translocation region. You generate flies with the following genotype:
N2(cy)/T2(cy+); N3(e)/T3(e+)
[N2 indicates a normal chromosome 2; T2 indicates a translocation chromosome with the centromere of chromosome 2 and a portion of chromosome 3; cy is the mutant allele associated with the curly wing phenotype, cy+ is the wild-type allele.] These flies have normal wings and normal body color.
a. Draw the pairing of these chromosomes during meiosis I.
b. Indicate the gametes that would be generated by alternate and adjacent-1 segregation patterns during meiosis I.
c. You mate two of these flies to one another. Indicate the expected genotypes and phenotypes (and their proportions) in the offspring.

Question 33

List the four basic types of chromosome rearrangements.

Question 34

Duchenne muscular dystrophy (DMD) is normally an X-linked recessive human disease affecting boys. Girls afflicted with DMD are rare. Cytogenetic studies of several girls with DMD have in each case revealed that these individuals carry X-autosome translocations. The autosomes vary, but the breakpoint on the X in every case is in band p21, which is the location of the DMD gene. Cytogenetic studies further revealed that in all cells studied in such DMD girls the normal X chromosome exists as a Barr body. How might these observations account for the existence of DMD-affected girls? Why is only the normal X, but not the translocated X, inactivated?

Question 35

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.

Question 36

How can a chromosome deletion be detected?

Question 37

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?

Question 38

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

Question 39

Which of the following chromosome rearrangements represents duplication?

A) A
B) B
C) C
D) D

Question 40

Isochromosomes have the structure ABC $\bullet$ CBA (where $\bullet$ represents the centromere and A, B, and C represent wild-type alleles of three different genes). In some cases, such isochromosomes are derived from two copies of one half of a metacentric chromosome, which has a centromere near its center. For example, a wild-type metacentric chromosome ABC $\bullet$ DEF might form two distinct isochromosomes, ABC $\bullet$ CBA and FED $\bullet$ DEF. The centromeres of such distinct isochromosomes can be homologous so that they cause the segregation of the two distinct isochromosomes from each other during meiosis.
a. A mutant of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF is viable. If you cross this mutant with a wild-type individual, what would you expect to be the genotype of the offspring? Would these offspring be viable or not? Explain.
b. What would you expect if you cross this mutant with another individual of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF? Explain.
c. You are given a pericentric inversion mutant in which this same chromosome is of genotype ABD $\bullet$ CEF. In an individual heterozygous for this inversion and a wild-type chromosome there is a crossover between C and the centromere. Draw the crossover event and indicate the gametes that would be generated.
d. Assume that the inversion interval is very small so that both duplications and deletions for this interval (from C to
D) do not cause inviability. Indicate the gentoypes expected in offspring of a cross between the inversion heterozygote and an individual of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF.

Question 41

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

A) disomy
B) inversion
C) nondisjunction
D) polyploidy
E) translocation

Question 42

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

Question 43

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

Question 44

Down syndrome has, in some cases, been found to run in families. Explain the genetic basis for this inherited form of the condition.

Question 45

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

Question 46

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

Question 47

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 a 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.

Question 48

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

Question 49

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

Question 50

In rare cases some children that express recessive genetic diseases, such as cystic fibrosis, have only one parent that is heterozygous for the disease allele. If the parents are the true biological parents of the affected child, offer a genetic explanation for this observation.

Question 51

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

Question 52

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

Question 53

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

Question 54

Which type of polyploidy is synonymous with amphidiploid?

A) allodiploid
B) allotriploid
C) autotriploid
D) allotetraploid
E) autotetraploid

Question 55

A man has a condition where all of his gametes undergo meiosis I normally, but there is nondisjunction of the sex chromosomes in 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

Question 56

Which type of aneuploidy is represented in gametes labeled B in the figure?

A) nullisomy
B) monosomy
C) trisomy
D) tetrasomy

Question 57

Which type of aneuploidy is represented in gametes labeled A in the figure?

A) nullisomy
B) monosomy
C) trisomy
D) tetrasomy

Question 58

You are studying the inheritance of the recessive red-spotted (r) trait in pea plants. You identify a phenotypically wild-type plant that, when crossed to a red-spotted plant, produces 5/6 wild-type offspring and 1/6 red-spotted offspring. When you look at the chromosomes of the wild-type plant, you note that it contains an extra copy of chromosome 2, which is where the red-spotted locus is located.
a. What is the genotype of the wild-type plant? What gametes will this plant generate? What are the genotypes of the wild-type and red-spotted offspring?
b. You identify a plant that you think is genotypically Rrr. If you cross this plant to an rr individual, what proportion of wild-type and red-spotted offspring would you expect?

Question 59

What are three ways that aneuploidy can arise?

Question 60

You are studying two different mutant fish lines (A and
B). You suspect that both have mutations that cause nondisjunction for a particular chromosome, which when aneuploid results in an altered egg phenotype. You notice that all of the eggs from the A mutants have the altered phenotype. In contrast, only half the eggs laid by B mutants have the altered phenotype. If you are right and the mutants are suffering nondisjunction during meiosis, what could explain the frequency difference in egg phenotype?

Question 61

Species I is diploid (2n = 6) with chromosomes AABBCC; a related species II is diploid (2n = 6) with chromosomes MMNNOO. Indicate the chromosomes that would be found in individuals with the following chromosome mutations.
a. trisomic for chromosome A
b. tetrasomic for chromosome N
c. an autotriploid of species I
d. an allotetraploid
e. an autotetraploid of species II
f. monosomic for chromosome B
g. a double trisomic for chromosomes A and C
h. a nullisomic for chromosome O

Question 62

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

Question 63

Species A and B are closely related. Species A has 2n = 12 chromosomes, and species B has 2n = 14 chromosomes. Chromosome numbers (2n) for the following related species are thought to have arisen through polyploidy. For each species, indicate what type of polyploid it is, and how it may have formed.
a. Species C 18
b. Species D 24
c. Species E 26
d. Species F 28
e. Species G 36
f. Species H 52
g. Species I 56

Question 64

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

Question 65

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

Question 66

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

Question 67

Explain the genetic basis for sterility in autopolyploid organisms.

Question 68

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