Genetic Analysis 2nd Edition by Sanders - Test Bank

Genetic Analysis 2nd Edition by Sanders – Test Bank

 

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Genetics: An Integrated Approach (Sanders)

Chapter 5   Genetic Linkage and Mapping in Eukaryotes

5.1   Multiple-Choice Questions

1)    Syntenic genes can assort independently when __________.

1. A) they are very close together on a chromosome
2. B) they are located on different chromosomes
3. C) crossing over occurs rarely between the genes
4. D) they are far apart on a chromosome and crossing over occurs frequently between the genes
5. E) they are far apart on a chromosome and crossing over occurs very rarely between the genes

Answer:  D

Section:  5.1

Skill:  Knowledge/Comprehension

2)    The alleles of linked genes tend to __________.

1. A) segregate together during gamete production
2. B) assort independently
3. C) be mutated more often than unlinked genes
4. D) experience a higher rate of crossing over
5. E) assort independently and show a higher rate of crossing over

Answer:  A

Section:  5.1

Skill:  Knowledge/Comprehension

3)    Genetic linkage leads to the production of a significantly greater than expected number of gametes containing chromosomes with __________.

1. A) allele combinations that are different from parental combinations
2. B) parental combinations of alleles
3. C) mutant alleles
4. D) dominant alleles
5. E) recessive alleles

Answer:  B

Section:  5.1

Skill:  Knowledge/Comprehension

4)    The syntenic genes A and Z are linked. A cross between two parents, AAZZ and aazz, produces F₁ progeny with the AaZz genotype. What are the possible arrangements of alleles on the F₁ progeny’s chromosomes?

1. A) AZ/az
2. B) Az/aZ
3. C) Aa/Zz
4. D) AZ/Az or az/aZ
5. E) A/Z or a/z

Answer:  A

Section:  5.1

Skill:  Application/Analysis

5)    In a dihybrid cross exhibiting complete genetic linkage, what would you expect?

1. A) one parental allele combination occurring more frequently than another
2. B) two equally frequent gametes containing only parental allele combinations
3. C) only recombinant gametes
4. D) one parental allele combination occurring more frequently than another and no recombinant gametes
5. E) two equally frequent gametes containing only parental allele combinations and no recombinant gametes

Answer:  E

Section:  5.1

Skill:  Application/Analysis

6)    In a two-point test-cross analysis, a dihybrid F₁ fly is crossed to a __________.

1. A) pure-breeding mate with a dominant phenotype (AABB)
2. B) pure-breeding mate with a recessive phenotype (aabb)
3. C) heterozygote mate (AaBb)
4. D) mate that is dominant for one gene and recessive for the other (AAbb or aaBB)
5. E) second dihybrid F₁ fly (sibling cross)

Answer:  B

Section:  5.1

Skill:  Knowledge/Comprehension

7)    In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F₁ progeny had a WT phenotype. Which of the following represents the arrangement of alleles on the F₁’s chromosome?

1. A) prvg/pr+vg+
2. B) pr+vg/prvg+
3. C) prpr+/vgvg+
4. D) prvg/prvg
5. E) pr+vg+/pr+vg+

Answer:  B

Section:  5.1

Skill:  Application/Analysis

8)    In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F₁ progeny had a WT phenotype. The recombination frequency between the two genes is 10%. If an F₁ individual was test crossed, what percentage of the progeny would you expect to have the WT phenotype?

 

1. A) 5%
2. B) 10%
3. C) 50%
4. D) 90%
5. E) 95%

Answer:  A

Section:  5.1

Skill:  Application/Analysis

9)    If you are given a recombination frequency of 34% between genes X and Y and 27% between X and Z, can you predict the order of the three genes?

1. A) Yes; the order is X-Z-Y.
2. B) Yes; the order is X-Y-Z.
3. C) Yes; the order is Z-X-Y.
4. D) No; based on this data alone, the order could be Z-Y-X or X-Y-Z.
5. E) No; based on this data alone, the order could be X-Z-Y or Z-X-Y.

Answer:  E

Section:  5.2

Skill:  Application/Analysis

10)  What type of test would you use to determine whether observed data constitute evidence of genetic linkage or are simply a case of chance variation from expected values?

1. A) test cross
2. B) two-point test cross
3. C) three-point test cross
4. D) chi-square analysis
5. E) recombination frequency (r) calculation

Answer:  D

Section:  5.2

Skill:  Knowledge/Comprehension

11)  You perform a test cross of the dihybrid AaBb and score the phenotypes of 1000 progeny. Assuming independent assortment, how many of the progeny do you expect to display the dominant phenotype for both the A and B genes?

1. A) 100
2. B) 200
3. C) 250
4. D) 500
5. E) 750

Answer:  C

Section:  5.2

Skill:  Application/Analysis

12)  Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes. How many different gamete genotypes are produced in a four-gene cross with incomplete genetic linkage?

1. A) 4
2. B) 8
3. C) 16
4. D) 20
5. E) 24

Answer:  C

Section:  5.3

Skill:  Application/Analysis

13)  Assuming three genes are linked, how many recombinant genotypes would you expect and at what frequency?

1. A) two recombinant genotypes, more frequent than expected by independent assortment
2. B) four recombinant genotypes, more frequent than expected by independent assortment
3. C) six recombinant genotypes, more frequent than expected by independent assortment
4. D) four recombinant genotypes, less frequent than expected by independent assortment
5. E) six recombinant genotypes, less frequent than expected by independent assortment

Answer:  E

Section:  5.3

Skill:  Knowledge/Comprehension

14)  For a given cross, the expected number of double recombinants is 20 and the observed number of double recombinants is 15. What is the coefficient of coincidence (c)?

1. A) 25
2. B) 33
3. C) 20
4. D) 75
5. E) 15

Answer:  D

Section:  5.3

Skill:  Application/Analysis

15)  For a given cross, the expected number of double recombinants is 20 and the observed number of double recombinants is 15. What is the interference calculation (I)?

1. A) 25
2. B) 33
3. C) 20
4. D) 75
5. E) 15

Answer:  A

Section:  5.3

Skill:  Application/Analysis

16)  Genes A and B are located 10cM from each other on a chromosome. Gene C is located 25cM from gene A and 15cM from gene B. Assuming that I = 0, what is the probability that the trihybrid ABC/abc will produce an ABC gamete?

76. A) 5%
77. B) 25%
78. C) 25%
79. D) 5%
80. E) .75%

Answer:  B

Section:  5.3

Skill:  Application/Analysis

17)  Genes A and B are located 10cM from each other on a chromosome. Gene C is located 25cM from gene A and 15cM from gene B. What is the probability that the trihybrid ABC/abc will produce any kind of recombinant gamete?

76. A) 5%
77. B) 25%
78. C) 5%
79. D) 5%
80. E) 75%

Answer:  C

Section:   5.3

Skill:  Application/Analysis

18)  Where does crossing over occur?

1. A) at the centromeres
2. B) at the telomeres
3. C) at nodules that occur randomly at “hotspots” along the synaptonemal complex
4. D) at nodules that occur in specific, evenly spaced locations along a chromosome
5. E) at both the centromeres and telomeres

Answer:  C

Section:  5.4

Skill:  Knowledge/Comprehension

19)  When does recombination occur?

1. A) before DNA replication
2. B) at the two-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and before DNA replication
3. C) at the four-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and before DNA replication
4. D) at the two-strand stage, when the sister chromatids have been separated, and after DNA replication
5. E) at the four-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and after DNA replication

Answer:  E

Section:  5.4

Skill:  Knowledge/Comprehension

20)  Which type of crossover event produces no recombinant chromosomes?

1. A) single-strand crossover
2. B) two-strand double crossover
3. C) three-strand double crossover
4. D) four-strand double crossover
5. E) None of the above; all crossover events produce recombinant chromosomes.

Answer:  B

Section:  5.4

Skill:  Knowledge/Comprehension

21)  Which type of crossover event produces two parental and two recombinant chromosomes in gametes?

1. A) single-strand crossover
2. B) two-strand double crossover
3. C) three-strand double crossover
4. D) four-strand double crossover
5. E) None of the above; all crossover events produce only recombinant chromosomes.

Answer:  C

Section:  5.4

Skill:  Knowledge/Comprehension

22)  Which type of crossover event produces all four recombinant chromosomes?

1. A) single-strand crossover
2. B) two-strand double crossover
3. C) three-strand double crossover
4. D) four-strand double crossover
5. E) None of the above; all crossover events produce a combination of parental and recombinant chromosomes.

Answer:  D

Section:  5.4

Skill:  Knowledge/Comprehension

23)  For a given haplotype, the frequencies of alleles for gene Y are Y = 0.65 and Y’ = 0.35, and the frequencies at gene Z are Z = 0.25 and Z’ = 0.75. What is the predicted frequency of the Y¢Z¢ haplotype?

1. A) 16
2. B) 26
3. C) 74
4. D) 84
5. E) 1

Answer:  B

Section:  5.6

Skill:  Application/Analysis

24)  Intragenic recombination can be detected __________.

1. A) based on recombination between homologs carrying different mutant alleles
2. B) by the recovery of 100% double-mutant chromosomes
3. C) by the recovery of both wild-type and double-mutant chromosomes
4. D) based on recombination between homologs with different mutant alleles and recovery of 100% double-mutant chromosomes
5. E) based on recombination between homologs with different mutant alleles and recovery of both wild-type and double-mutant chromosomes

Answer:  E

Section:  5.4

Skill:  Application/Analysis

25)  After analysis of 100 pedigrees, the Z_max from the analysis of linkage between a disease gene D and the DNA marker P was found to be 3.5 at θ = 0.25. Which of the following is the best interpretation of these results?

1. A) No conclusion can be made regarding linkage of D and P.
2. B) The evidence supports linkage of D and P at 25 cM.
3. C) The evidence supports linkage of D and P at 2.5 cM.
4. D) The evidence supports linkage of D and P at 0.25 cM.
5. E) The evidence indicates that D and P are not linked.

Answer:  B

Section:  5.5

Skill:  Application/Analysis

26)  The Z_max from the analysis of a disease gene N and the DNA marker H was 2.5 at θ = 0.1. Which of the following is the best interpretation of this result?

1. A) N and H are not linked.
2. B) N and H are separated by 10 cM.
3. C) N and H are separated by more than 10 cM.
4. D) N and H are separated by less than 10 cM.
5. E) No conclusion can be made regarding the linkage of N and H.

Answer:  E

Section:  5.5

Skill:  Application/Analysis

5.2   Short-Answer Questions

1)    What is observed when syntenic genes are close enough to one another that they are unable to assort independently?

Answer:  genetic linkage

Section:  5.1

Skill:  Knowledge/Comprehension

2)    What is the term for chromosomes that do not reshuffle the alleles of linked genes?

Answer:  parental chromosomes

Section:  5.1

Skill:  Knowledge/Comprehension

 

3)    Recombination analysis allows for the mapping of genes because the frequency of crossing over is proportional to what distance?

Answer:  distance between genes

Section:  5.1

Skill:  Knowledge/Comprehension

4)    What organism exhibits complete genetic linkage, meaning there is no recombination between homologous chromosomes?

Answer:  male Drosophila or Diptera

Section:  5.1

Skill:  Knowledge/Comprehension

5)    Incomplete genetic linkage is far more common than complete linkage. What is the term for gametes produced when recombination shuffles the alleles of linked genes?

Answer:   nonparental or recombinant gametes

Section:  5.1

Skill:  Knowledge/Comprehension

6)    Two genes, A and X, exhibit incomplete linkage. The frequency of each parental gamete (AX and ax) is 45%. What is the approximate frequency of the Ax gamete?

Answer:  5%

Section:  5.1

Skill:  Application/Analysis

7)    There are three genes located in the gene order A-B-C on a chromosome. Would you expect the recombination frequency to be higher between A and B or A and C?

Answer:  higher between A and C (they are farther apart)

Section:  5.1

Skill:  Application/Analysis

8)    Morgan realized that Bateson and Punnett had detected genetic linkage but they couldn’t explain their results because they performed the wrong cross. What type of cross did Morgan use for the analysis of genetic linkage of autosomal genes in Drosophila?

Answer:  two-point test-cross analysis

Section:  5.1

Skill:  Knowledge/Comprehension

9)    In a two-point test-cross analysis, what are the “two points” being tested?

Answer:  the two genes

Section:  5.1

Skill:  Knowledge/Comprehension

10)  What unit of physical distance between genes on a chromosome provides a convenient way to relate the recombination frequencies for linked genes with their positions and order along a chromosome?

Answer:  map unit (m.u.) or centimorgan (cM)

Section:  5.2

Skill:  Knowledge/Comprehension

11)  What type of test would you use to determine the relative order of more than two genes?

Answer:  three-point test-cross

Section:  5.3

Skill:  Knowledge/Comprehension

12)  In most tests of genetic linkage, the number of double crossovers is less than the number expected due to what effect, which limits the number of crossovers that can occur in a short length of chromosome?

Answer:  interference (I)

Section:  5.3

Skill:  Knowledge/Comprehension

13)  Refer to this map to answer the questions:

1. a) What is the distance between gene E and gene F?
2. b) Assuming I = 0, what is the probability of no crossovers between gene D and gene E?
3. c) Assuming I = 0, what is the probability of no crossovers between gene E and gene F?
4. d) Considering both gene pairs, what is the proportion of nonrecombinant gametes?
5. e) What is the predicted frequency of each parental gamete (DEF/def )?
6. f) What is the recombination frequency between gene D and gene E?
7. g) What is the recombination frequency between gene E and gene F?
8. h) What is the frequency of two single recombinant gametes between genes D and E?
9. i) What is the frequency of two single recombinant gametes between genes E and F?
10. j) What is the frequency of each of the double-recombinant gametes, DeF and dEf?
11. k) Fill in the blanks below to prove that the sum of the frequencies of the eight predicted gamete genotypes is equal to 1.0:

_______ + _______ + _______ + _______ + _______ + _______ + _______ + _______ = 1

DEF            def             Def            dEF            DEf            deF            DeF           dEf

Answer:  a)  12 cM

1. b) 92%
2. c) 88%
3. d) (0.92)(0.88) = 0.8096
4. e) (0.5)(0.8096) = 0.4048
5. f) 8%
6. g) 12%
7. h) (0.08)(0.88)(0.5) = 0.0352
8. i) (0.12)(0.92)(0.5) = 0.0552
9. j) (0.08)(0.12)(0.5) = 0.0048
10. k) 4048 + 0.0048 + 0.0352 + 0.0352 + 0.0552 + 0.0552 + 0.0048 + 0.0048 = 1

Section:  5.3

Skill:  Synthesis/Evaluation

14)  When constructing a genetic map of Zea mays, Creighton and McClintock used genetic markers as well as structural differences in the homologous copies of chromosome 9 that can be seen under the microscope. What are these structural differences called?

Answer:  cytological markers

Section:  5.4

Skill:  Knowledge/Comprehension

15)  What is the highest possible frequency of recombination between linked genes that can be generated by any type of crossover event?

Answer:  50%

Section:  5.4

Skill:  Knowledge/Comprehension

16)  Recombination frequency between linked genes increases as the distance between genes gets larger or gets smaller?

Answer:  larger

Section:  5.4

Skill:  Knowledge/Comprehension

17)  Recombination frequency differs between males and females. Which sex has a higher rate of recombination, heterogametic (males) or homogametic (females)?

Answer:  homogametic (females)

Section:  5.4

Skill:  Knowledge/Comprehension

18)  If there is a maximum Lod score of 4.2 at θ = 0.31, what can you say about the linkage and the distance between two genes?

Answer:  linked and 31 cM apart

Section:  5.5

Skill:  Application/Analysis

19)  If too little time has passed for crossing over to randomize haplotypes or if natural selection favors certain haplotypes, what would you expect to see?

Answer:  linkage disequilibrium

Section:  5.6

Skill:  Knowledge/Comprehension

20)  Ascospores in yeast are not arranged in a particular order. Thus, the four haploid ascospores contained within a yeast ascus are known as what?

Answer:  unordered tetrad

Section:  5.7

Skill:  Knowledge/Comprehension

 

5.3   Fill-in-the-Blank Questions

1)    A chromosome with a different combination of alleles than parental that is created by crossing over between homologous chromosomes is termed ________.

Answer:  recombinant chromosome

Section:  5.1

Skill:  Knowledge/Comprehension

2)    Alleles of linked genes usually segregate together during meiosis. When they don’t, it is because ________ has occurred between them.

Answer:  crossing over

Section:  5.1

Skill:  Knowledge/Comprehension

3)    Genetic linkage can be spotted by comparing the observed frequencies of ________ with the frequencies expected (assuming independent assortment).

Answer:  gamete genotypes/progeny phenotypes

Section:  5.1

Skill:  Knowledge/Comprehension

4)    5% recombination is equal to ________ map unit(s) (m.u.) or centimorgan(s) (cM) of distance between linked genes.

Answer:  5

Section:  5.2

Skill:  Application/Analysis

5)    The specific array of alleles making up a set of linked genes on a single chromosome is called a ________.

Answer:  haplotype

Section:  5.6

Skill:  Knowledge/Comprehension

5.4   Essay Questions

1)    What is the relationship between linked genes and syntenic genes? Are syntenic genes always linked?Are linked genes always syntenic? Describe what is meant by each term.

Answer:  Linked genes are always inherited together with no independent assortment. Syntenic genes are genes found on the same chromosome. Linked genes are always found on the same chromosome, but they are unable to sort independently because there is no crossing over observed between these two genes. Syntenic genes can be unlinked, and their alleles will assort independently if they are far enough apart on the chromosome for crossing over to generate independent assortment of the alleles.

Section:  5.1

Skill:  Synthesis/Evaluation

 

2)    The mapping of the human genome in the mid-1980s was integral for identifying new human genetic markers because of the identification of what types of polymorphic DNA markers?

Answer:  SNPs and restriction fragments

Section:  5.5

Skill:  Knowledge/Comprehension

3)    Describe why allelic phase is a major obstacle in mapping human genes.

Answer:  Allelic phase is the arrangement of different alleles of linked genes on homologous parental chromosomes. Allelic phase is required for genetic linkage analysis because you need to know which alleles are unique to “parental” and “recombinant” gametes.

Section:  5.5

Skill:  Synthesis/Evaluation

4)    How is Newton Morton’s statistical method helpful for calculating the overall probability of genetic linkage when allelic phase is unknown?

Answer:  Morton’s method determines whether genetic linkage exists between genes for which allelic phase is unknown by comparing the likelihood of obtaining the genotypes and phenotypes observed in a pedigree if two genes are linked versus the likelihood of getting the same pedigree structure if the genes assort independently. This approach assesses the probability of genetic linkage between two genes at a time and compares the probability of genetic linkage to the probability of independent assortment of the genes.

Section:  5.5

Skill:  Synthesis/Evaluation

5)    What is the Lod score?

Answer:  The ratio of the two likelihoods described in answer 4 above gives the “odds” of genetic linkage, and the Logarithm of the odds ratio generates the Lod score, a statistical value representing the probability of genetic linkage between two genes. A Lod score is a statistic that can attain significance favoring genetic linkage if the probability of genetic linkage is sufficiently greater than the probability of independent assortment, or significance against genetic linkage if the probability of independent assortment is sufficiently greater than the linkage probability. Lod scores can be interpreted for individual families, or they can be added together for as many families as are analyzed.

Section:  5.5

Skill:  Knowledge/comprehension

6)    What would a Lod score of 3.2 tell you about genetic linkage? What information does the θ value tell you?

Answer:  Scores of greater than 3.0 provide evidence of genetic linkage. θ values that correspond to a significant Lod score indicate an approximate distance (in cM) between linked genes.

Section:  5.5

Skill:  Synthesis/Evaluation

7)    Describe the three types of tetrads that can be formed when a diploid yeast sporulates to form haploid gametes.

Answer:  Parental ditypes (PD) contain four haploid cells with the same alleles seen in the parental class.

Nonparental ditypes (NPD) contain four recombinant haploid cells because the two parental alleles have recombined to form a nonparental combination of alleles.

Tetratype tetrads (TT) contain four different kinds of haploid cells: two parental spores and two recombinant spores. When two genes are not linked, tetratypes arise when a crossover occurs between one of the two genes and its centromere.

Section:  5.7

Skill:  Application/Analysis

8)    What ratios of these three tetrads would you expect to see if two genes are linked? Why is each type of tetrad more or less common? What ratios would you expect to see if the two genes are unlinked? Why?

Answer:  If two genes are linked, you will see that PD > TT > NPD. PD tetrads are most common; they are produced when no crossover occurs between genes and when two-strand double crossover takes place. TT tetrads are less frequent than PD; they occur when single crossovers or three-strand double crossovers take place. NPD tetrads are least frequent; they form only when four-strand double crossover occurs.

If PD = NPD, then the two genes are unlinked. This ratio indicates that either the genes are located on different chromosomes or they are syntenic but very far apart.

Section:  5.7

Skill:  Synthesis/Evaluation

9)    The products of meiosis yield the following results:

PD = 1200                        TT = 750                     NPD = 50

What is the recombination frequency?

Answer:

RF  = [(NPD + 1/2TT)/total # tetrads] × 100

= [(50 + 1/2(750)/2000] × 100

= 21.25 m.u.

Section:  5.7

Skill:  Synthesis/Evaluation

10)  Crossing over occurs frequently during meiosis. Can crossing over occur during mitosis? Explain why mitotic crossing over may or may not be possible.

Answer:  Mitotic crossover is a rare event. Mitotic crossing over occurs only in diploid (somatic) cells; thus, to study mitotic crossing over in a haploid organism, diploid cells have to be created artificially. Mitotic crossing over most likely occurs when homologous chromosomal segments are accidentally paired in somatic cells since it requires that after DNA replication, but before homologous chromosomes randomly align along the metaphase plate, the homologous chromosomes come together and interact like chromosomes during prophase I in meiosis. Opportunities for this unusual kind of mitotic interaction are rare but variable by species. Although rare, mitotic crossing over is important in some organisms. Some fungi that do not have a sexual cycle use mitotic crossing over to introduce genetic variation. In humans, mitotic crossing over is thought to be important in allowing recessive cancer-causing mutations such as RB.

Section:  5.8

Skill:  Synthesis/Evaluation