Deck 5: Chromosome Mapping in Eukaryotes

Question 1

Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome?

A)the genes are very far apart on the same chromosome,such that there is always a crossover between them
B)the genes are very close together on the chromosome,such that there is never a crossover between them
C)too large a sample size
D)the genes are very far apart on the same chromosome,such that there is never a crossover between them
E)a mating between consanguineous individuals

Answer 1

A

Question 2

The genes for purple eyes and curved wings are approximately 21 map units apart on chromosome II in Drosophila.Assume that a purple-eyed female was mated to a curved wing male and that the resulting F₁ phenotypically wild-type females were mated to purple,curved males.Of 1000 offspring,what would be the expected number of flies with purple eyes and curved wings?

A)540
B)395
C)210
D)790
E)105

Answer 2

395

Question 3

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data,one can conclude that .

A)the G and E loci are segregating independently
B)the G and E loci are linked
C)the G and E loci reside on the same chromosome over 50 map units apart
D)the G and E loci show complete linkage
E)the G and E loci assort independently

Answer 3

the G and E loci are linked

Question 4

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data one can conclude that______ .

A)the recombinant progeny are Ge/Ge and gE/gE
B)the recombinant progeny are gE/ge and Ge/ge
C)the recombinant progeny are GE/GE and ge/ge
D)the recombinant progeny are gE/GE and GE/ge
E)the recombinant progeny are GE/ge and GE/ge

Question 5

Phenotypically wild-type F₁ female Drosophila,whose mothers had light eyes lt and fathers had straw stw bristles,produced the following offspring when crossed to homozygous light-straw males: Compute the map distance between the light and straw loci.

A)4 map units
B)98 map units
C)12 map units
D)8 map units
E)2 map units

Question 6

Who was the student in Morgan's laboratory who first realized that the sequence of genes could be determined by Morgan's proposal that two genes located relatively close to each other are less likely to form chiasma between them than if the two genes were relatively far apart?

A)Charles Darwin
B)Barbara McClintock
C)Thomas Hunt
D)A)H.Sturtevant
E)Gregor Mendel

Question 7

At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?

A)during synapsis in prometaphase
B)at the four-strand stage of meiosis,after synapsis of homologous chromosomes,and before the end of prophase I
C)in S phase of meiosis
D)during synapsis at the four-strand stage of meiosis
E)during bivalent formation,after synapsis of homologous chromosomes,and before the end of prophase I

Question 8

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body.The F₁ Lobe females were then backcrossed with homozygous smooth abdomen,straw body males,the following phenotypes were observed:

A)smooth,Lobe,straw
B)it is impossible to tell
C)Lobe,smooth,straw
D)smooth,straw,Lobe
E)Lobe,straw,smooth

Question 9

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data,one can conclude that there are map units between the G and E loci.

A)15
B)25
C)10
D)5
E)20

Question 10

Choose the true statement below.

A)When two genes are over 50 map units apart,a crossover can theoretically occur 100% of the time.
B)The percentage of tetrads involved in exchange between two genes is equal to the number of recombinant progeny seen.
C)Linkage viewed from results of typical crosses always occurs when two loci are on the same chromosome.
D)When two genes are over 50 map units apart,a crossover would theoretically occur 0% of the time.
E)A single crossover on a chromosome will always yield the recombinant phenotype of the genes you are interested in.

Question 11

Which of the following statements is true?

A)The linkage ratio is best seen in genes on nonhomologous chromosomes.
B)If two gene loci are on nonhomologous chromosomes,genes at these loci are expected to assort independently.
C)Linkage without crossing over leads to all recombinant chromosomes.
D)The chromosomal theory of inheritance denotes that linked alleles will never be separated.
E)A centromere and its surrounding genes constitute a linkage group.

Question 12

Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb,48 Aabb,52 aaBb,94 aabb.These results are consistent with which of the following?

A)sex-linked inheritance with 30% crossing over
B)independent assortment
C)linkage with approximately 33 map units between the two gene loci
D)100% recombination
E)linkage with 50% crossing over

Question 13

Assume that the genes for tan body and bare wings are 15 map units apart on chromosome II in Drosophila.Assume also that a tan-bodied,bare-winged female was mated to a wild-type male and that the resulting F₁ phenotypically wild-type females were mated to tan-bodied,bare-winged males.Of 1000 offspring,what would be the expected of wild-type offspring,and in what numbers would they be expected?

A)75
B)425
C)50
D)350
E)8

Question 14

What term is applied when two genes fail to assort independently,that is,they tend to segregate together during gamete formation?

A)tetrad analysis
B)Mendelian inheritance
C)discontinuous inheritance
D)dominance and/or recessiveness
E)linkage

Question 15

Below is a diagram during crossing over.Describe the outcome.

A)offspring will not look like either parent
B)a 1:1 ratio
C)formation of parental alleles only
D)segregation of alleles A and a during meiosis II
E)segregation of alleles A and a during meiosis I

Question 16

Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism.If you examined 200 primary oocytes,in how many would you expect to see a chiasma between the two loci mentioned above?

A)96
B)48
C)6
D)12
E)24

Question 17

What is the relationship between the degree of crossing over and the distance between two genes?

A)There is no correlation.
B)It is direct: as the distance decreases,the frequency of recombination increases.
C)It is indirect: as the distance decreases,the frequency of recombination doubles.
D)It is indirect: as the distance increases,the frequency of recombination doubles.
E)It is direct: as the distance increases,the frequency of recombination increases.

Question 18

If complete linkage occurs,we expect ______.

A)to see all four types of offspring
B)a 1:1:1:1 ratio in the test cross
C)to see only parental phenotypes in the F₂ of the appropriate test cross
D)to see only recombinant phenotypes in the F₂ of the appropriate test cross
E)a 9:3:3:1 ratio in the F₂

Question 19

Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb,Aabb,aaBb,aabb.These results are consistent with which of the following?

A)alternation of generations
B)incomplete dominance
C)hemizygosity
D)independent assortment
E)complete linkage

Question 20

A ____ is all the genes on a single chromosome.

A)chromosomal conglomeration
B)gene loci line
C)genetic allele formation
D)linkage group
E)recombination group

Question 21

What is a lod score?

A)determination of the probability that two traits are linked by analyzing pedigrees
B)determination of how often a gene mapping experiment gives the correct results
C)a method using cell fusion to determine on which chromosome a gene resides
D)a calculation to show how much interference is occurring in crossover formation
E)determination of how often double crossovers occur

Question 22

In a three-point mapping experiment,which class do you expect to find the least?

A)recombinant
B)noncrossover
C)parental
D)double crossover
E)single crossover

Question 23

In the fruit fly,Drosophila melanogaster,a spineless no wing bristles female fly is mated to a male that is claret dark eyes and hairless no thoracic bristles .Phenotypically wild-type F₁ female progeny were mated to fully homozygous mutant males,and the following progeny 1000 total were observed:

-
What are the map distances between hairless and spineless?

A)50
B)10
C)40
D)30
E)45

Question 24

In the fruit fly,Drosophila melanogaster,a spineless no wing bristles female fly is mated to a male that is claret dark eyes and hairless no thoracic bristles).Phenotypically wild-type F₁ female progeny were mated to fully homozygous mutant males,and the following progeny 1000 total were observed:

-
What is the gene order?

A)spineless,claret,hairless
B)claret,hairless,spineless
C)it is impossible to tell
D)claret,spineless,hairless
E)hairless,spineless,claret

Question 25

Methods for determining the linkage group and genetic map in humans involve which of the following?

A)twin spots and tetrad analysis
B)tetrad analysis and bromodeoxyuridine
C)chiasma-type and classical analyses
D)zygotene and pachytene DNA syntheses
E)DNA markers

Question 26

Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb,48 Aabb,52 aaBb,94 aabb.These results are consistent with which scenario described?

A)It is impossible to tell.
B)There is a very high coefficient of coincidence.
C)The genes are unlinked.
D)In the AaBb parent,the dominant alleles are on one homolog and the recessive alleles are on the other.
E)In the AaBb parent,each homolog has one dominant allele and one recessive allele.

Question 27

What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?

A)the inclusion of the X and Y chromosomes in SNP experiments
B)positive interference
C)the use of synteny
D)negative interference
E)the genome sequence of a species

Question 28

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body.The F₁ Lobe females were then backcrossed with homozygous smooth abdomen,straw body males,the following phenotypes were observed: Give the map units between Lobe and straw.

A)15
B)7.5
C)10
D)20
E)5

Question 29

The phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called________ .

A)negative interference
B)reciprocal genetic exchange
C)mitotic recombination
D)positive interference
E)chiasma

Question 30

Assume that two genes are 80 map units apart on chromosome II of Drosophila and that a cross is made between a doubly heterozygous female and a homozygous recessive male.What percent recombination would be expected in the offspring of this type of cross?

A)30
B)5
C)50
D)100
E)80

Question 31

What two terms apply to the fusion of cultured human and mouse cells that produces cell lines that are useful in assigning a gene to a particular human chromosome?

A)forward and reverse
B)lod score and pod score
C)positive and negative
D)single and double
E)heterokaryon and synkaryon

Question 32

In a three-point mapping experiment,how many different genotypic classes are expected?

A)1
B)0
C)8
D)4
E)2

Question 33

__________occurs when a crossover in one region of a chromosome reduces crossovers in nearby regions.

A)Triple crossover
B)Negative supercoiling
C)Coefficient of coincidence
D)Positive interference
E)Negative interference

Question 34

The coefficient of coincidence reflects the frequency of observed double crossovers compared to the frequency of expected double crossovers.What is the relationship between the coefficient of coincidence and interference?

A)Interference equals the coefficient of coincidence.
B)Interference equals the coefficient of coincidence divided by the map units calculated.
C)Interference is the inverse square of the coefficient of coincidence.
D)Interference is one minus the coefficient of coincidence.
E)Interference is recombinants minus nonrecombinants.

Question 35

In Drosophila,assume that the gene for scute bristles s)is located at map position 0.0 and that the gene for ruby eyes r)is at position 15.0.Both genes are located on the X chromosome and are recessive to their wild-type alleles.A cross is made between scute-bristled females and ruby-eyed males.Phenotypically wild-type F₁ females were then mated to homozygous double mutant males,and 1000 offspring were produced.Give the frequency of scute expected.

A)360
B)500
C)75
D)425
E)250

Question 36

Three loci,mitochondrial malate dehydrogenase that forms a and b MDHa,MDHb ,glucuronidase that forms 1 and 2 GUS1,GUS2 ,and a histone gene that forms + and - H⁺,H^- ,are located on chromosome #7 in humans.Assume that the MDH locus is at position 35,GUS at position 45,and H at position 75.A female whose mother was homozygous for MDHa,GUS2,and H⁺ and whose father was homozygous for MDHb,GUS1,and H^- produces a sample of 1000 egg cells.Give the expected numbers of the MDHa GUS2 H^- cells she would produce.Assume no chromosomal interference.

A)15
B)235
C)315
D)135
E)0

Question 37

Which of the following best describes why mapping is most accurate when genes are close together on a chromosome?

A)This is not true; mapping genes is most accurate when genes are far away from each other.
B)Double crossover events yield a result that looks the same as no crossover in a two gene mapping experiment and this throws off the calculations.
C)The centromere gets in the way.
D)This is not true; relative distance of two loci on a chromosome has no effect on accuracy of mapping.
E)Double crossover events yield a result that looks the same as one crossover in a two gene mapping experiment and this throws off the calculations.

Question 38

If interference is complete,what would be the frequency of double crossovers?

A)0.75
B)2
C)0
D)1
E)0.25

Question 39

Which of the following is an example of positive interference?

A)Double crossovers do not occur.
B)A single crossover stimulates further recombination.
C)Crossovers will not occur near centromeres.
D)An actively transcribed gene is less likely to undergo crossover than a quiescent one.
E)A crossover in one region inhibits crossovers in nearby regions.

Question 40

What is a physical map of a chromosome?

A)identification of the length of the chromosome by comparing it to known chromosomes
B)description of the base pair difference between two loci
C)determination of the p and q arm length
D)determination of where the centromere lies
E)determination of how far apart genes are my recombination mapping

Question 41

Which of the following statements is true?

A)Sister chromatid exchange would mutate one strand of DNA.
B)Harlequin chromosomes are a result of homologous recombination.
C)Sister chromatid exchange would lead to a reshuffling of alleles.
D)Crossing over has a cytological basis.
E)Exchanges occur between homologous chromosomes,but never between sister chromatids.

Question 42

Sister chromatid exchanges increase in frequency in the presence of X-rays,certain viruses,ultraviolet light,and certain chemical mutagens.In what autosomal recessive disorder is there known to be an increase in sister chromatid exchanges?

A)cystic fibrosis
B)Harlequin syndrome
C)achondroplasia
D)Huntington's disease
E)Bloom syndrome

Question 43

Based on the classic experiments of Creighton and McClintock with maize,crossing over involves a physical exchange between chromatids.What particular chromosomal characteristic allowed their experiments to succeed?

A)a missing chromosome
B)a chromosome with a unique cytological marker
C)three chromosomes with identical structure
D)colored bands along the lengths of a chromosome
E)an extra chromosome