Deck 5: Linkage, Recombination, and the Mapping of Genes on Chromosomes

Question 1

In Drosophila, singed bristles (sn) and cut wings (ct) are both caused by recessive, X-linked alleles.The wild type alleles (sn⁺ and ct⁺) are responsible for straight bristles and intact wings, respectively.A female homozygous for sn and ct⁺ is crossed to a sn⁺ct male.The F₁ flies are interbred.The F₂ males are distributed as follows What is the map distance between sn and ct?

A)12 m.u.
B)13 m.u.
C)25 m.u.
D)50 m.u.
E)75 m.u.

Answer 1

25 m.u.

Question 2

Which of the three genes, if any, is unlinked to the others?

A)T/t
B)R/r
C)W/w
D)All three genes are linked.

Answer 2

W/w

Question 3

Suppose the L and M genes are on the same chromosome but separated by 100 map units.What fraction of the progeny from the cross LM/lm * lm/lm would be Lm/lm?

A)10%
B)25%
C)50%
D)75%
E)100%

Answer 3

25%

Question 4

Which statement(s) below apply to the concept of gene linkage?
A.The different alleles of two or more genes that are on a chromosome are inherited in an manner inconsistent with Mendel's Second law
B.Recombination between homologous chromosomes during meiosis results in different combinations of alleles for different genes
C.Recombination between sister chromatids during meiosis results in different combinations of alleles for different genes

A)A only
B)B only
C)C only
D)A and B
E)A, B, and C

Question 5

If only 100 progeny had been counted and the same proportion observed, how would the p value and the conclusion drawn about linkage change?

A)The p value would increase, and the likelihood of linkage increases.
B)The p value would decrease, and the likelihood of linkage increases.
C)Neither the p value nor the likelihood of linkage would change.
D)The p value would decrease, and the likelihood of linkage decreases.

Question 6

Which of the following linkage maps correctly shows the order and distance between the px, sp, and cn genes?

A)sp--0.21 mu--px--30.01 mu--cn
B)sp--30.01 mu--px--0.21 mu--cn
C)sp--0.2 mu--px--30 mu--cn
D)px--0.2 mu--sp--30.2 mu--cn
E)px--30.2 mu--sp--0.2 mu--cn

Question 7

The pairwise map distances for four linked genes are as follows: A-B = 22 m.u., B-C = 7 m.u., C-D = 9 m.u., B-D = 2 m.u., A-D = 20 m.u., A-C = 29 m.u.What is the order of these four genes?

A)ABCD
B)ADBC
C)ABDC
D)BADC
E)CADB

Question 8

Given this data, which of the following is the most accurate range within which the p value falls, and what can be concluded?

A)0 < p < 0.01, genes C and D are most likely unlinked.
B)0 < p < 0.01, genes C and D are most likely linked.
C)0.01 < p < 0.05, genes C and D are most likely linked.
D)0.01 < p < 0.05, genes C and D are most likely unlinked.

Question 9

What is the genotype of the females that gave rise to these progeny?

A)px⁺ sp cn / px sp⁺ cn⁺
B)px⁺ sp cn⁺ / px sp⁺ cn
C)px⁺ sp⁺ cn⁺ / px sp cn
D)px sp cn⁺ / px⁺ sp⁺ cn
E)Insufficient data

Question 10

If two or more of the genes are linked, what map distance separates them?

A)4 mu
B)12 mu
C)24 mu
D)50 mu
E)None of the genes are linked to each other.

Question 11

What is the genotype of the tall, red, wide-leaved parent?

A)Tt Rr Ww
B)Tt Rr WW
C)TT RR WW
D)TT Rr Ww
E)TT RR Ww

Question 12

How many degrees of freedom are there?

A)1
B)2
C)3
D)4

Question 13

What is the coefficient of coincidence in this region?

A)0
B)0.2
C)0.4
D)0.6
E)0.8

Question 14

If the map distance between genes A and B is 10 map units and the map distance between genes B and C is 25 map units, what is the map distance between genes A and C?

A)15 map units
B)35 map units
C)either 15 map units or 35 map units, depending on the order of the genes
D)The map distance between A and C can not be predicted from these data.

Question 15

Which of the three genes is in the middle?

A)px
B)sp
C)cn
D)Insufficient data

Question 16

The R/r and S/s genes are linked and 10 map units apart.In the cross Rs/rS * rs/rs what fraction of the progeny will be RS/rs?

A)5%
B)10%
C)25%
D)40%
E)45%

Question 17

Calculate the $\chi$ ² value used test the hypothesis that the C and D genes are unlinked.

A)0
B)0.0576
C)10.8
D)14.4
E)Cannot be determined

Question 18

In Drosophila, singed bristles (sn) and cut wings (ct) are both caused by recessive, X-linked alleles.The wild type alleles (sn⁺ and ct⁺) are responsible for straight bristles and intact wings, respectively.A female homozygous for sn and ct⁺ is crossed to a sn⁺ct male.The F₁ flies are interbred.The F₂ males are distributed as follows Of these 4 phenotypic classes of offspring, which of the following arose from a parental gamete produced by the F1 females?

A)sn⁺ ct⁺ and sn⁺ ct flies
B)sn⁺ ct⁺ flies only
C)sn ct and sn⁺ ct⁺ flies
D)sn⁺ ct and sn ct⁺ flies
E)sn ct and sn ct⁺ flies

Question 19

Which of the following linkage maps correctly shows the order and distance between the y, f, and v genes?

A)f--35 mu--y--15 mu--v
B)f--22 mu--y--15 mu--v
C)y--35 mu--f--22 mu--v
D)y--22 mu--v--15 mu--f
E)y--15 mu--v--22 mu--f

Question 20

Calculate the coefficient of coincidence in this region.

A)0
B)0.16
C)0.33
D)0.5
E)0.66

Question 21

The cross Lpq / lPQ * lpq / lpq is carried out and the L gene is found to be in the middle.What would be the genotypes of the double crossover gametes in this cross?

A)LPQ and lpq
B)LpQ and lPq
C)lpQ and LPq
D)Lpq and lPQ
E)cannot be determined

Question 22

The map of a chromosome interval is: A--10 mu--B--40 mu--C
From the cross Abc / aBC * abc / abc, how many double crossovers would be expected out of 1000 progeny?

A)5
B)10
C)20
D)40
E)80

Question 23

Suppose a three-point testcross was conducted involving the genes X, Y, and Z.If the most abundant classes are XYz and xyZ and the rarest classes are xYZ and Xyz, which gene is in the middle?

A)X
B)Y
C)Z
D)cannot be determined

Question 24

In tetrad analysis, NPD asci result from

A)independent assortment of unlinked genes.
B)double crossovers between linked genes.
C)single crossovers between linked genes.
D)single crossovers between a gene and a centromere.
E)independent assortment of unlinked genes or double crossovers between linked genes.

Question 25

The zipper-like connection between paired homologs in early prophase is known as a

A)spindle fiber.
B)synaptic junction.
C)synaptonemal complex.
D)chiasma.
E)none of the choices are correct.

Question 26

In tetrad analysis, the criterion for linkage of two genes is

A)NPD = T.
B)PD = T.
C)PD = NPD.
D)PD > NPD.
E)PD > T.

Question 27

In Drosophila, the genes y (yellow body) and car (carnation eyes) are located at opposite ends of the X chromosome.In doubly heterozygous females (y⁺ car⁺ / y car), a single chiasma is observed somewhere along the X chromosome in 90% of the examined oocytes.No X chromosomes with multiple chiasmata are observed.What percentage of the male progeny from such a female would be recombinant for y and car?

A)5%
B)10%
C)45%
D)55%
E)90%

Question 28

In tetrad analysis, second-division segregations result from

A)single crossovers between linked genes.
B)double crossovers between linked genes.
C)single crossovers between a gene and a centromere.
D)independent assortment of unlinked genes.
E)nondisjunction of homologs.

Question 29

Genes Q and R are 20 map units apart.If a plant of genotype QR / qr is selfed, what percentage of the progeny will be qr in phenotype?

A)4%
B)10%
C)16%
D)20%
E)40%

Question 30

A dihybrid test cross is made between genes H and I.Four categories of offspring are produced: HI, Hi, hI, and hi.You wish to use the $\chi$ ² test to test the hypothesis that the H and I genes are unlinked.How many degrees of freedom would there be in this test?

A)1
B)2
C)3
D)4
E)0

Question 31

In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b--30 mu--c--20 mu--sp
This region exhibits 90% interference.How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

A)3
B)6
C)54
D)60
E)600

Question 32

Tetrad analysis shows that crossing over occurs at the four-strand stage (i.e., after replication) because, when two genes are linked,

A)NPD > T.
B)T > NPD.
C)T > PD.
D)PD > NPD.
E)PD > T.

Question 33

Which of the following processes can generate recombinant gametes?

A)Segregation of alleles in a heterozygote.
B)Crossing over between two linked heterozygous loci.
C)Independent assortment of two unlinked heterozygous loci.
D)Crossing over between two linked heterozygous loci and independent assortment of two unlinked heterozygous loci
E)Segregation of alleles in a heterozygote, crossing over between two linked heterozygous loci and independent assortment of two unlinked heterozygous loci

Question 34

The R/r and S/s genes are linked and 10 map units apart.In the cross Rs / rS * rs / rs what percentage of the progeny will be Rs / rs?

A)5%
B)10%
C)25%
D)40%
E)45%

Question 35

The measured distance between genes D and E in a two point test cross is 50 map units.What does this mean in physical terms?

A)D and E are on different pairs of chromosomes.
B)D and E are linked and exactly 50 map units apart.
C)D and E are linked and at least 50 map units apart.
D)either D and E are on different pairs of chromosomes or D and E are linked and exactly 50 map units apart
E)either D and E are on different pairs of chromosomes or D and E are linked and at least 50 map units apart

Question 36

Suppose an individual is heterozygous for a pair of alleles (e.g., A/a).Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)

A)The crossover would have to occur between the A locus and the centromere and involve two homologous (non-sister) chromatids.
B)The crossover would have to occur between the A locus and the end of the chromosome and involve two homologous (non-sister) chromatids.
C)The crossover would have to occur on the same chromosome arm as the A locus and involve two homologous (non-sister) chromatids.
D)The crossover would have to occur on the same chromosome as the A locus and involve two homologous (non-sister) chromatids.
E)The crossover would have to occur between the A locus and the centromere and involve two sister chromatids (not homologous) chromatids.

Question 37

The Q gene locus is 10 map units from the R gene locus which is 40 map units from the S gene locus: Q--10 mu--R--40 mu--S
Which interval would likely show the higher ratio of double to single chiasmata?

A)Q-R
B)R-S
C)The ratios would be the same in the two intervals.
D)Two chiasmata never occur in the same interval.

Question 38

Recombination frequencies near 50% suggest that

A)two genes are on different chromosomes.
B)two genes lie very close together on the same chromosome.
C)two genes are on the same chromosome but lie very far apart.
D)two genes are on different chromosomes, or two genes are on the same chromosome but lie very far apart.
E)none of the choices are correct.

Question 39

Crossing over takes place in paired bivalents consisting of ______ chromatids, and involves _______ of the chromatids.

A)2, 2
B)2, 4
C)4, 2
D)4, 4
E)8, 4

Question 40

Sturtevant's detailed mapping studies of the X chromosome of Drosophila established what genetic principle?

A)That genes are arranged in a linear order on the chromosomes.
B)That genes are carried on chromosomes.
C)That sex determination is controlled by the X and Y chromosomes.
D)That segregation of an allelic gene pair is accompanied by disjunction of homologous chromosomes.
E)That different pairs of chromosomes assort independently.

Question 41

What is the map distance between the pr and cn genes?

A)20 m.u.
B)2 m.u.
C)4 m.u.
D)46 m.u.
E)8 m.u.

Question 42

What is the p value from this test? (Pick the most accurate choice.)

A)p > 0.5
B)0.1 < p < 0.5
C)p < 0.1
D)p < 0.05
E)p < 0.01

Question 43

A crossover that would result in genetic recombination (e.g., Abc or aBC) could involve which chromatids?

A)1 & 2 or 3 & 4
B)1 & 3 or 2 & 4
C)1 & 4 or 2 & 3
D)1 & 3 or 1 & 4 or 2 & 3 or 2 & 4
E)any two of the four chromatids

Question 44

What is the $\chi$ ² value for a test of the null hypothesis?

A)0.5
B)1.0
C)2.0
D)0.4
E)20

Question 45

The mother of these progeny resulted from a cross between two flies from true breeding lines.What are the genotypes of these two lines?

A)pr pr cn⁺ cn⁺ and pr⁺ pr⁺ cn cn
B)pr⁺ pr⁺ cn⁺ cn⁺ and pr pr cn cn
C)pr⁺ pr cn⁺ cn and pr pr cn cn
D)pr⁺ pr cn cn and pr pr cn⁺ cn
E)Either pr pr cn⁺ cn⁺ and pr⁺ pr⁺ cn cn or pr⁺ pr⁺ cn⁺ cn⁺ and pr pr cn cn could be true.

Question 46

What is the genotype of the mother of these progeny?

A)pr cn / pr⁺ cn⁺
B)pr⁺ cn / pr⁺ cn
C)pr⁺ cn / pr cn⁺
D)pr cn⁺ / pr cn⁺
E)pr cn / pr cn

Question 47

Which of the following types of tetrads contain two recombinant and two parental asci?

A)PD only
B)PD and NPD
C)T only
D)PD and T
E)NPD and T

Question 48

Which classes are the parental types?

A)wild-type and orange
B)brown and bright-red
C)wild-type and brown
D)bright-red and orange
E)There is no way to determine this.

Question 49

If an individual is heterozygous at two loci (Ab/aB) which are on the same chromosome arm with the A locus closest the centromere under what conditions would a crossover in a somatic cell generate a twin spot?

A)The crossover would have to occur between the A locus and the centromere locus and involve two homologous (non-sister) chromatids.
B)The crossover would have to occur between the A locus and the B locus and involve two homologous (non-sister) chromatids.
C)The crossover would have to occur between the B locus and the end of the chromosome locus and involve two homologous (non-sister) chromatids.
D)A double crossover would have to occur, with one crossover between the A locus and the centromere and a second crossover between the A and B loci locus and both crossovers would have to involve two homologous (non-sister) chromatids.
E)No crossover in a somatic cell could generate a twin spot.

Question 50

his4/TRP1; his4/TRP1; HIS4/trp1; HIS4/trp1

A)PD
B)NPD
C)T
D)Cannot be determined

Question 51

HIS4/trp1; HIS4/trp1; his4/TRP1; his4/TRP1

A)PD
B)NPD
C)T
D)Cannot be determined

Question 52

What happens physically during the process of crossing over?

A)Two homologous chromatids break and rejoin at random sites along the chromosome.
B)The genetic information on one chromatid is replaced by copying genetic information from a homologous chromatid without there being any physical exchange between the chromosomes.
C)Two homologous chromatids break and rejoin at precisely the same site along the chromosome so that there is no loss or gain of material on either product.
D)It is not known what occurs during crossing over.

Question 53

A woman whose mother is colorblind and whose father has hemophilia A is pregnant with a boy and what is the probability that the baby will have normal vision and blood clotting?

A)0.03
B)0.15
C)0.485
D)0.47
E)0.015

Question 54

Suppose a woman has four sons, and two are colorblind but have normal blood clotting and two have hemophilia but normal color vision.What is the probable genotype of the woman?

A)HR / hr
B)Hr / hr
C)hr / hR
D)Hr / hR
E)HR / Hr

Question 55

his4/TRP1; his4/trp1; HIS4/trp1; HIS4/TRP1

A)PD
B)NPD
C)T
D)Cannot be determined

Question 56

HIS4/trp1; HIS4/TRP1; his4/TRP1; his4/trp1

A)PD
B)NPD
C)T
D)Cannot be determined

Question 57

his4/trp1; his4/trp1; HIS4/TRP1;HIS4/TRP

A)PD
B)NPD
C)T
D)Cannot be determined

Question 58

Some of the larger human chromosomes typically contain multiple chiasmata during meiotic prophase.If you were to carefully study the distribution of these chiasmata, what would you find?

A)Chiasmata are randomly distributed along chromosomes.
B)All chromosome pairs have the same number of chiasmata.
C)A single chromosome pair always has the same number of chiasmata in every meiotic cell.
D)Chiasmata are spaced along a chromosome arm more regularly than would be expected by chance.
E)Chiasmata are spaced more irregularly along a chromosome arm than would be expected by chance.

Question 59

Individuals heterozygous for the RB⁺ and RB^- alleles can develop tumors as a result of

A)a mitotic crossover that leads to homozygosity for both RB⁺ and RB^-.
B)a somatic mutation in the RB⁺ allele that leads to homozygosity for RB^-.
C)a somatic mutation in the RB^- allele that leads to homozygosity for RB⁺.
D)the fact that RB^- is dominant to RB⁺.
E)a mitotic crossover that leads to homozygosity for both RB⁺ and RB^- and a somatic mutation in the RB⁺ allele that leads to homozygosity for RB^-.

Question 60

Assume a double crossover occurs in this pair of chromosomes that results in chromatids of the genotype AbC and aBc.If the first crossover (the one between A and B) involves chromatids 1 & 4, which chromatids could be involved in the second crossover?

A)1 & 2 or 3 & 4
B)1 & 3 or 2 & 4
C)1 & 4 or 2 & 3
D)1 & 3 or 1 & 4 or 2 & 3 or 2 & 4
E)any two of the four chromatids

Question 61

ws⁺; ws⁺; ws⁺; ws⁺; ws; ws; ws; ws

A)First-division segregation pattern
B)Second-division segregation pattern

Question 62

If the p value corresponding to a given $\chi$ ² value and number of degrees of freedom exceeds 0.05, then the null hypothesis is rejected and it is predicted that the two genes being evaluated are not linked.

Question 63

The hypothesis that predicts no linkage between genes is known as the null hypothesis.

Question 64

ws⁺; ws⁺; ws; ws; ws⁺; ws⁺; ws; ws

A)First-division segregation pattern
B)Second-division segregation pattern

Question 65

Chiasmata are structures of cross over between sister chromatids of homologous chromosomes.

Question 66

Genes that are not syntenic are not linked.

Question 67

The length of an entire linkage group or chromosome may exceed 50 mu because the map distance is calculated from the addition of the distance between many gene pairs.

Question 68

A coefficient of coincidence of 0.5 in a region of three genes means that half as many double crossovers were observed as would have been expected if crossovers in the two intervals were independent.

Question 69

ws; ws; ws⁺; ws⁺; ws⁺; ws⁺; ws; ws

A)First-division segregation pattern
B)Second-division segregation pattern

Question 70

A linkage group can be defined as genes that may be so far apart on a chromosome that they cannot be shown to be linked directly but they can be shown to be on the same chromosome due to their linkage with other genes.

Question 71

A female mouse from a true-breeding wild-type strain was crossed to a male mouse with apricot eyes (ap) and grey body (gy).The F₁ mice were wild-type for both traits.When the F₁ were interbred, the F₂ were distributed as follows: Which of the following statements is correct?

A)ap and gy are unlinked.
B)ap and gy are linked on an autosome and 10 map units apart.
C)ap and gy are linked on an autosome and 20 map units apart.
D)ap and gy are X-linked and 10 map units apart.
E)ap and gy are X-linked and 20 map units apart.

Question 72

Suppose the map for a particular human chromosome interval is: a--1 mu--b--1 mu--c--1 mu--d--1 mu--e--1 mu--f
In a man heterozygous for all six genes, what fraction of his sperm would be recombinant in the a-f interval?

A)0%
B)1%
C)2.5%
D)5%
E)Cannot be determined

Question 73

Chiasmata can be seen through a light microscope and are sites of recombination.

Question 74

Fungi that produce tetrads typically grow as haploids but can undergo sexual reproduction by combining different mating types.

Question 75

Two genes are considered linked when F₂ progeny more commonly show the recombinant genotype.

Question 76

Large sectors suggest a mitotic recombination event late in the growth of a yeast colony.

Question 77

ws; ws; ws⁺; ws⁺; ws; ws; ws⁺; ws⁺

A)First-division segregation pattern
B)Second-division segregation pattern

Question 78

ws; ws; ws; ws; ws⁺; ws⁺; ws⁺; ws⁺

A)First-division segregation pattern
B)Second-division segregation pattern

Question 79

Sectors with a different phenotype in an otherwise uniform yeast colony may be evidence of mitotic recombination.

Question 80

In an ordered octad, every spore is adjacent to at least one spore that is genetically identical to itself.