Deck 5: Genetic Linkage and Mapping in Eukaryotes
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Deck 5: Genetic Linkage and Mapping in Eukaryotes
1
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)?
A)0.25
B)1.33
C)20
D)0.75
E)15
A)0.25
B)1.33
C)20
D)0.75
E)15
D
2
In a dihybrid cross exhibiting complete genetic linkage,what would you expect?
A)one parental allele combination occurring more frequently than another
B)two equally frequent gametes containing only parental allele combinations
C)only recombinant gametes
D)one parental allele combination occurring more frequently than another and no recombinant gametes
E)two equally frequent gametes containing only parental allele combinations and no recombinant gametes
A)one parental allele combination occurring more frequently than another
B)two equally frequent gametes containing only parental allele combinations
C)only recombinant gametes
D)one parental allele combination occurring more frequently than another and no recombinant gametes
E)two equally frequent gametes containing only parental allele combinations and no recombinant gametes
E
3
When does recombination occur?
A)before DNA replication
B)at the two-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
C)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
D)at the two-strand stage,when the sister chromatids have been separated,and after DNA replication
E)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and after DNA replication
A)before DNA replication
B)at the two-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
C)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
D)at the two-strand stage,when the sister chromatids have been separated,and after DNA replication
E)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and after DNA replication
E
4
Which type of crossover event produces no recombinant chromosomes?
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce recombinant chromosomes.
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce recombinant chromosomes.
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5
Genetic linkage leads to the production of a significantly greater than expected number of gametes containing chromosomes with
A)allele combinations that are different from parental combinations.
B)parental combinations of alleles.
C)mutant alleles.
D)dominant alleles.
E)recessive alleles.
A)allele combinations that are different from parental combinations.
B)parental combinations of alleles.
C)mutant alleles.
D)dominant alleles.
E)recessive alleles.
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6
Intragenic recombination can be detected
A)based on recombination between homologs carrying different mutant alleles.
B)by the recovery of 100% double-mutant chromosomes.
C)by the recovery of both wild-type and double-mutant chromosomes.
D)based on recombination between homologs with different mutant alleles and recovery of 100% double-mutant chromosomes.
E)based on recombination between homologs with different mutant alleles and recovery of both wild-type and double-mutant chromosomes.
A)based on recombination between homologs carrying different mutant alleles.
B)by the recovery of 100% double-mutant chromosomes.
C)by the recovery of both wild-type and double-mutant chromosomes.
D)based on recombination between homologs with different mutant alleles and recovery of 100% double-mutant chromosomes.
E)based on recombination between homologs with different mutant alleles and recovery of both wild-type and double-mutant chromosomes.
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7
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?
A)0.16
B)0.26
C)0.74
D)0.84
E)1.1
A)0.16
B)0.26
C)0.74
D)0.84
E)1.1
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8
Assuming three genes are linked,how many recombinant genotypes would you expect and at what frequency?
A)two recombinant genotypes,more frequent than expected by chance
B)four recombinant genotypes,more frequent than expected by chance
C)six recombinant genotypes,more frequent than expected by chance
D)four recombinant genotypes,less frequent than expected by chance
E)six recombinant genotypes,less frequent than expected by chance
A)two recombinant genotypes,more frequent than expected by chance
B)four recombinant genotypes,more frequent than expected by chance
C)six recombinant genotypes,more frequent than expected by chance
D)four recombinant genotypes,less frequent than expected by chance
E)six recombinant genotypes,less frequent than expected by chance
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9
Syntenic genes can assort independently when
A)they are very close together on a chromosome.
B)they are located on different chromosomes.
C)crossing over occurs rarely between the genes.
D)they are far apart on a chromosome and crossing over occurs frequently between the genes.
E)they are far apart on a chromosome and crossing over occurs very rarely between the genes.
A)they are very close together on a chromosome.
B)they are located on different chromosomes.
C)crossing over occurs rarely between the genes.
D)they are far apart on a chromosome and crossing over occurs frequently between the genes.
E)they are far apart on a chromosome and crossing over occurs very rarely between the genes.
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10
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)?
A)0.25
B)1.33
C)20
D)0.75
E)15
A)0.25
B)1.33
C)20
D)0.75
E)15
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11
Where does crossing over occur?
A)at the centromeres
B)at the telomeres
C)at nodules that occur randomly at "hotspots" along the synaptonemal complex
D)at nodules that occur in specific,evenly spaced locations along a chromosome
E)at both the centromeres and telomeres
A)at the centromeres
B)at the telomeres
C)at nodules that occur randomly at "hotspots" along the synaptonemal complex
D)at nodules that occur in specific,evenly spaced locations along a chromosome
E)at both the centromeres and telomeres
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12
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?
A)AZ/az
B)Az/aZ
C)Aa/Zz
D)AZ/Az or az/aZ
E)A/Z or a/z
A)AZ/az
B)Az/aZ
C)Aa/Zz
D)AZ/Az or az/aZ
E)A/Z or a/z
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13
The Huntington disease (HD)allele was discovered
A)by mapping it to blood enzyme genes,based on Lod scores of -2.
B)through pedigree analysis alone.
C)by linkage to a DNA genetic marker,D4S10 with a Lod score of 8.53.
D)through mapping to known homologs in other organisms such as mice.
E)through direct sequencing of mutations identified by SNPs.
A)by mapping it to blood enzyme genes,based on Lod scores of -2.
B)through pedigree analysis alone.
C)by linkage to a DNA genetic marker,D4S10 with a Lod score of 8.53.
D)through mapping to known homologs in other organisms such as mice.
E)through direct sequencing of mutations identified by SNPs.
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14
The alleles of linked genes tend to
A)segregate together during gamete production.
B)assort independently.
C)be mutated more often than unlinked genes.
D)experience a higher rate of crossing over.
E)assort independently and show a higher rate of crossing over.
A)segregate together during gamete production.
B)assort independently.
C)be mutated more often than unlinked genes.
D)experience a higher rate of crossing over.
E)assort independently and show a higher rate of crossing over.
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15
Which type of crossover event produces all four recombinant chromosomes?
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce a combination of parental and recombinant chromosomes.
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce a combination of parental and recombinant chromosomes.
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16
In a two-point test-cross analysis,a dihybrid F₁ fly is crossed to a
A)pure-breeding mate with a dominant phenotype (AABB).
B)pure-breeding mate with a recessive phenotype (aabb).
C)heterozygote mate (AaBb).
D)mate that is dominant for one gene and recessive for the other (AAbb or aaBB).
E)second dihybrid F₁ fly (sibling cross).
A)pure-breeding mate with a dominant phenotype (AABB).
B)pure-breeding mate with a recessive phenotype (aabb).
C)heterozygote mate (AaBb).
D)mate that is dominant for one gene and recessive for the other (AAbb or aaBB).
E)second dihybrid F₁ fly (sibling cross).
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17
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?
A)test cross
B)two-point test-cross
C)three-point test-cross
D)chi-square analysis
E)recombination frequency (r)calculation
A)test cross
B)two-point test-cross
C)three-point test-cross
D)chi-square analysis
E)recombination frequency (r)calculation
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18
Which type of crossover event produces two parental and two recombinant chromosomes in gametes?
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce only recombinant chromosomes.
A)single-strand crossover
B)two-strand double crossover
C)three-strand double crossover
D)four-strand double crossover
E)None of the above;all crossover events produce only recombinant chromosomes.
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19
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?
A)Yes;the order is X-Z-Y.
B)Yes;the order is X-Y-Z.
C)Yes;the order is Z-X-Y.
D)No;based on this data alone,the order could be Z-Y-X or X-Y-Z.
E)No;based on this data alone,the order could be X-Z-Y or Z-X-Y.
A)Yes;the order is X-Z-Y.
B)Yes;the order is X-Y-Z.
C)Yes;the order is Z-X-Y.
D)No;based on this data alone,the order could be Z-Y-X or X-Y-Z.
E)No;based on this data alone,the order could be X-Z-Y or Z-X-Y.
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20
Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes.How many genotypes are produced in a four-gene cross with incomplete genetic linkage?
A)4
B)8
C)16
D)20
E)24
A)4
B)8
C)16
D)20
E)24
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21
What unit of physical distance between genes on a chromosome provides a convenient way to link the recombination frequencies for linked genes with their positions and order along a chromosome?
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22
Recombination analysis allows for the mapping of genes because the frequency of crossing over is proportional to what?
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23
Chromosomes that do not reshuffle the alleles of linked genes are identified as what?
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24
If there is a maximum Lod score of 4.2 at = 0.31,what can you say about the linkage and the distance between two genes?
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25
Morgan realized that Bateson and Punnett had detected genetic linkage but 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?
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26
What organism exhibits complete genetic linkage,meaning there is no recombination between homologous chromosomes?
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27
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?
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28
What type of test would you use to determine the relative order of more than two genes?
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29
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?
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30
Does recombination frequency between linked genes increase as the distance between genes gets larger or smaller?
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31
In a two-point test-cross analysis,what are the "two points" being tested?
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32
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?
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33
What is the highest possible frequency of recombination between linked genes that can be generated by any type of crossover event?
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34
If too little time has passed for crossing over to randomize haplotypes or if natural selection favors certain haplotypes,what type of linkage would you expect to see?
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35
Refer to this map to answer the following questions:
a) What is the distance between gene E and gene F?
b) Assuming I = 0,what is the probability of no crossovers between gene D and gene E?
c) Assuming I = 0,what is the probability of no crossovers between gene E and gene F?
d) Considering both gene pairs,what is the proportion of nonrecombinant gametes?
e) What is the predicted frequency of each parental gamete (DEF/def)?
f) What is the recombination frequency between gene D and gene E?
g) What is the recombination frequency between gene E and gene F?
h) What is the frequency of two single recombinant gametes between genes D and E?
i) What is the frequency of two single recombinant gametes between genes E and F?
j) What is the frequency of each of the double-recombinant gametes,DeF and dEf?
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

a) What is the distance between gene E and gene F?
b) Assuming I = 0,what is the probability of no crossovers between gene D and gene E?
c) Assuming I = 0,what is the probability of no crossovers between gene E and gene F?
d) Considering both gene pairs,what is the proportion of nonrecombinant gametes?
e) What is the predicted frequency of each parental gamete (DEF/def)?
f) What is the recombination frequency between gene D and gene E?
g) What is the recombination frequency between gene E and gene F?
h) What is the frequency of two single recombinant gametes between genes D and E?
i) What is the frequency of two single recombinant gametes between genes E and F?
j) What is the frequency of each of the double-recombinant gametes,DeF and dEf?
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
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36
Bateson and Punnett saw early evidence of gene linkage.What terms did they use to describe genes that remained together frequently and the loss of parental alleles in favor of new,nonparental phenotypes in the F₂ progeny?
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37
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?
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38
What is observed when syntenic genes are so close to one another that they are unable to assort independently?
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39
Recombination frequency differs between males and females.Which sex has a higher rate of recombination,heterogametic (males)or homogametic (females)?
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40
Incomplete genetic linkage is far more common than complete linkage.Recombination between the homologs produces what type(s)of gametes?
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41
Describe why allelic phase is a major obstacle in mapping human genes.
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42
The alleles of syntenic genes can be reshuffled by crossing over between homologous chromosomes to produce ________.
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43
The specific array of alleles making up a set of linked genes on a single chromosome is called a ________.
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44
Genetic linkage can be spotted by comparing the observed frequencies of ________ with the frequencies expected (assuming independent assortment).
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45
Ascospores in yeast are not arranged in a particular order.Thus,the four haploid ascospores contained within a yeast ascus are known as what?
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46
What is the Lod score?
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47
Describe the three types of tetrads.
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48
What is the relationship between linked genes and syntenic genes? Are syntenic genes always linked,or are linked genes always syntenic? Describe what is meant by each term.
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49
What would a Lod score of 3.2 tell you about genetic linkage? What information does the Θ value tell you?
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50
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?
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51
Crossing over occurs frequently during meiosis.Can crossing over occur during mitosis? Explain why mitotic crossing over may or may not be possible.
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52
What ratios of these three tetrads would you expect to see if two genes are linked or unlinked? Why is one type of tetrad more or less common?
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53
How is Newton Morton's statistical method helpful for calculating the overall probability of genetic linkage when allelic phase is unknown?
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54
The products of meiosis yield the following results:
PD = 1200 TT = 750 NPD = 50
What is the recombination frequency?
PD = 1200 TT = 750 NPD = 50
What is the recombination frequency?
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55
The tendency of alleles of linked genes to segregate together during meiosis can be broken by ________.
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56
In early genetic analysis,5% recombination is equal to ________ map unit(s)(m.u.)or centimorgan(s)(cM)of distance between linked genes.
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