Deck 4: Mapping Eukaryote Chromosomes by Recombination

Question 1

A diploid plant is a trihybrid for flower color (gene "F"),leaf size (gene "L")and seed weight (gene "S");its phenotype includes red flowers,large leaves,and heavy seeds.This plant is crossed to a tester plant (which has white flowers,small leaves,and light seeds).The progeny is as follows:

$\begin{array}{|l|l|}\hline23 \text { Red, heavy, large } & 232 \text { White, heavy, large } \\\hline 25 \mathrm{Red}, \text { heavy, small } & 228 \text { White, heavy, small } \\\hline 230 \mathrm{Red} \text {, light, large } & 25 \text { White, light, large } \\\hline 235 \mathrm{Red} \text {, light, small } & 26 \text { White, light, small }\\\hline\end{array}$
What can be concluded about the linkage relationships of the three genes in question?

A)Genes F,L,and S are linked.
B)Genes F and L are linked,while S assorts independently.
C)Genes F and S are linked,while L assorts independently.
D)Genes S and L are linked,while F assorts independently.
E)Genes F,L,and S are unlinked and assort independently.

Answer 1

Genes F and S are linked,while L assorts independently.

Question 2

In a diploid invertebrate,genes D and E are closely linked.Single crossovers between these two genes occurs only in 1 out of 40 meioses,and multiple crossovers are never observed.If an individual has the genotype D e/d E,what percentage of its gametes are expected to be recombinant (either DE or de)?

A)1.25%
B)2.5%
C)4%
D)5%
E)20%

Answer 2

1.25%

Question 3

Out of 800 progeny of a three-point testcross,there were 16 double crossover recombinants,whereas 80 had been expected on the basis of no interference.The interference is:

A)0.690.
B)0.310.
C)0.155.
D)0.80.
E)0.40.

Answer 3

0.80.

Question 4

The maize genes sh and bz are linked,40 map units apart.If a plant sh⁺bz/sh bz⁺ is selfed,what proportion of the progeny will be sh bz/sh bz?

A)0.04
B)0.10
C)0.20
D)0.40
E)0.50

Question 5

A male mouse of genotype A/a ^. B/b is testcrossed multiple times.Overall,these testcrosses produce 11 mice of phenotype A B,81 A b,77 a B,and 14 a b.Based on these data,the genotypes of the male mouse's parents are most likely:

A)A/a;B/b and A/a;B/b.
B)AB/AB and ab/ab.
C)AB/ab and AB/ab.
D)Ab/Ab and aB/aB.
E)Ab/ab and Ab/ab.

Question 6

The F,G,and H loci are linked in the order written.There are 30 map units between F and G,and 30 map units between G and H.If a plant F G H/f g h is testcrossed,what proportion of progeny plants will be f g h/f g h if there is no interference?

A)0.70
B)0.30
C)0.245
D)0.21
E)0.15

Question 7

In Drosophila,the genes crossveinless-c and Stubble are linked,about 7 map units apart on chromosome 3.cv-c is a recessive mutant allele of crossveinless-c (cv-c⁺ is wild type),while Sb is a dominant mutant allele of Stubble (Sb⁺ is wild type). A dihybrid female Drosophila with genotype cv-c Sb⁺/cv-c⁺Sb is testcrossed.The proportion of phenotypically wild-type individuals in the progeny of the testcross will be:

A)0.035.
B)0.070.
C)0.350.
D)0.465.
E)0.930.

Question 8

The linkage relationships among the four mouse genes,A,B,C,and D,are shown in the map below.



What proportion of the eggs produced by a female mouse with genotype Ab/aB;CD/cd will carry all the recessive alleles?

A)0.064
B)0.075
C)0.150
D)0.250
E)0.255

Question 9

In an experimental plant,the genes t and q are linked.A pure breeding t/t individual is crossed to a pure breeding q/q individual to obtain a dihybrid F₁.Genotypically,the F₁ individuals can be described as:

A)complementary dihybrids.
B)crossover dihybrids.
C)dihybrids in cis.
D)recombinant dihybrids.
E)dihybrids in trans.

Question 10

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is selfed and an F₂ is obtained.Which of the following ratios most likely represents the phenotypic ratio observed in this F₂?

A)1:1:1:1
B)1:4:4:1
C)9:3:3:1
D)51:24:24:1
E)66:9:9:16

Question 11

A dihybrid in cis is crossed to a dihybrid in trans (the two genes of interest,A and B,are linked).What proportion of the progeny is expected to be homozygous recessive with respect to the two genes of interest?

A)less than 6.25%
B)more than 6.25%,but less than 18.75%
C)about 18.75%
D)more than 18.75%,but less than 37.5%
E)more than 37.5%

Question 12

Two genes,A and B,are linked.An individual of genotype A b/A b is crossed to one that is a B/a B.The F₁ is testcrossed.Which of the following ratios most likely represents the phenotypic ratio observed in the progeny of this testcross?

A)1:1:1:1
B)1:4:4:1
C)9:3:3:1
D)51:24:24:1
E)66:9:9:16

Question 13

A sweet pea plant of genotype A/A ^. B/B is crossed to one that is a/a ^. b/b to produce a dihybrid F₁.One cell of one F₁ individual (genotype A/a ^. B/b)goes through meiosis and produces four gametes of the following genotypes: A ^. b,A ^. b,a ^.B and a ^.B.What can be concluded regarding the linkage relationship between the two genes?

A)Genes A and B are linked;the result is indicative of linkage as the gametes are recombinants.
B)Genes A and B are linked;the result is indicative of linkage as the gametes are the products of crossovers.
C)Genes A and B could be linked or unlinked;the result is not indicative of either,because in both cases it's possible to obtain 100% recombinant gametes from one meiosis.
D)Genes A and B could be linked or unlinked;the result is unusual as we should never obtain more than 50% recombinants from one meiosis.
E)Genes A and B are unlinked;the result is indicative of independent assortment as only two genotypes are represented among the gametes.

Question 14

In Drosophila,the two genes w and sn are X-linked and 25 map units apart.A female fly of genotype w⁺sn⁺/w sn is crossed to a male from a wild-type line.What percent of male progeny will be w⁺sn?

A)0%
B)12.5%
C)25%
D)37.5%
E)50%

Question 15

The mouse autosomal genes B and S are linked and 38 map units apart.Genotypes B S/B S and b s/b s are intercrossed,and the F₁ is testcrossed to b s/b s.The proportion of B-S- progeny will be:

A)0.19.
B)0.31.
C)0.50.
D)0.38.
E)0.76.

Question 16

The three genes,D,E,and F,are closely linked as indicated on the map below.In this region of the genome,there is no interference (the coefficient of coincidence is 1).



If a trihybrid with genotype ABC/abc is testcrossed,what is the expected percent of "parentals" within the progeny?

A)8.5%
B)15%
C)42.5%
D)85%
E)85.5%

Question 17

A plant of genotype C/C ^. d/d is crossed to c/c ^. D/D,and the F₁ is testcrossed.If the genes in question are linked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be:

A)less than 25%.
B)about 25%.
C)more than 25% but less than 50%.
D)about 50%.
E)more than 50% but less than 75%.

Question 18

In maize,two plants that are both heterozygous for the recessive alleles a and b are crossed.What frequency of double-mutant progeny will appear if a and b are 7.2 map units apart,and both parents carry a and b in repulsion (trans)?

A)0.001296
B)0.005184
C)0.036
D)0.0625
E)0.072

Question 19

A plant of genotype C/C ;d/d is crossed to c/c ;D/D,and the F₁ is testcrossed.If the genes in question are unlinked,the percentage of double homozygous recessive individuals in the offspring of the testcross will be:

A)less than 25%.
B)about 25%.
C)more than 25%,but less than 50%.
D)about 50%.
E)more than 50% but less than 75%.

Question 20

In maize,the genes W and D are so tightly linked that virtually no crossovers occur between them.A dihybrid W d/w D is testcrossed to w d/w d.The percent of progeny with W-/D- phenotype will be:

A)0.
B)25.
C)50.
D)75.
E)100.

Question 21

Neurospora loci d and f are located on the same chromosome.The d locus always segregates at M_I,while the e locus segregates at M_II at a frequency of 10%.Assuming complete interference,the distance between loci d and f is:

A)5 map units.
B)10 map units.
C)20 map units.
D)40 map units.
E)45 map units.

Question 22

In an unordered ascus analysis of the Neurospora loci cot and fl,there were 42 tetratypes and 8 nonparental ditypes out of a total of 290 asci.These loci are linked at a distance of:

A)2 m.u.
B)5 m.u.
C)10 m.u.
D)21 m.u.
E)25 m.u.

Question 23

Ascospores from a cross leu-2 * ad-7 met-3 (all auxotrophic markers)are plated on minimal medium (no adenine,leucine,or methionine).If the three genes are unlinked,what proportion of ascospores is expected to grow into a colony on this medium?

A)0.005
B)0.045
C)0.125
D)0.250
E)0.500

Question 24

In loppins (small,diploid invertebrates),chocolate-dependent problem-solving ability is an autosomal recessive trait.You have been hired to map the position of the gene controlling this phenotype (called "lu")using two SSLP markers (called "A" and "B").You first cross two pure-breeding loppins:

lu⁺A^{[3 repeats]} B^{[5 repeats]}/lu^+-A^{[3 repeats]} B^{[5 repeats]} X lu^- A^{[6 repeats]} B^{[8 repeats]}/lu^-A^{[6 repeats]} B^{[8 repeats]}
The F₁ is then crossed back to the lu^-/lu^- parent.Which of the following results would indicate that the lu gene is much closer to SSLP "A" than to SSLP "B"?

A)lower proportion of A^{[3 repeats]}B^{[5 repeats]}/A^{[3 repeats]}B^{[5 repeats]} than A^{[3 repeats]}B^{[8 repeats]}/A^{[3 repeats]}B^{[5 repeats]} individuals
B)lower proportion of lu⁺A^{[3 repeats]}/lu^-A^{[6 repeats]} than lu⁺A^{[3 repeats]}/lu^-A^{[3 repeats]} individuals
C)lower proportion of lu⁺A^{[3 repeats]}/lu^-A^{[6 repeats]} than lu⁺A^{[6 repeats]}/lu^-A^{[6 repeats]} individuals
D)lower proportion of lu⁺A^{[6 repeats]}/lu^-A^{[3 repeats]} than lu⁺B^{[8 repeats]}/lu^-B^{[8 repeats]} individuals
E)lower proportion of lu⁺A^{[6 repeats]}/lu^-A^{[6 repeats]} than lu⁺B^{[8 repeats]}/lu^-B^{[8 repeats]} individuals

Question 25

The maximum second division segregation frequency normally possible is:

A)25%.
B)33.3%.
C)50%.
D)66.7%.
E)100% .

Question 26

Ascospores from a cross a $\times$ b c (all auxotrophic markers)are analyzed.If genes b and c are linked,10 map units apart,but gene a is located on a different chromosome,what proportion of ascospores is expected to be a⁺b⁺c⁺?

A)about 12.5%
B)about 22.5%
C)about 25%
D)about 45%
E)about 50%

Question 27

A corn plant known to be hybrid for three linked genes is testcrossed.The progeny phenotypes and frequencies are: $$\begin{array} { | l | l | } \hline + + + & 74 \\\hline a b c & 70 \\\hline a + + & 44 \\\hline + b c & 50 \\\hline + + c & 4 \\\hline a b + & 2 \\\hline a + c & 368 \\\hline + b + & 388 \\\hline\end{array}$$
The coefficient of coincidence in this genomic region is:

A)0.06.
B)0.15.
C)0.40.
D)0.44.
E)1.36 .

Question 28

Ascospores from a cross of c $\times$ d e (all auxotrophic markers)are analyzed.If genes c and d are linked,10 map units apart,but gene e is located on a different chromosome,what proportion of ascospores is expected to be c⁺d⁺e⁺?

A)about 1%
B)about 2.5%
C)about 5%
D)about 40%
E)about 50%

Question 29

In a linear tetrad analysis,the second division segregation (M_II)frequency of the cyh locus is 16%.The map distance from this locus to its centromere is:

A)4 m.u.
B)8 m.u.
C)16 m.u.
D)32 m.u.
E)50 m.u.

Question 30

In a haploid organism,the loci leu and arg are linked,30 map units apart.In a cross of leu⁺arg * leu arg⁺,what proportion of progeny will be leu arg?

A)0
B)0.05
C)0.10
D)0.15
E)0.30

Question 31

A second-division segregation ascus is an indication of:

A)absence of linkage between centromere and locus.
B)a crossover between centromere and locus.
C)a four-strand crossover between centromere and locus.
D)interference in the region between centromere and locus
E)a two-strand double crossover between centromere and locus.

Question 32

Below is a pedigree for a very rare,late-onset genetic condition.Below the pedigree are represented the RFLP banding patterns obtained for each individual in the family.The RFLP locus used is about 2 cM away from the gene responsible for the disease.Note that darker/thicker bands indicate homozygosity for that particular morph of the RFLP.
What is the probability that the child in generation III will develop the disease?

A)0%
B)0.4%
C)1%
D)2%
E)50%

Question 33

An SSLP is located 2 map units away from the X-linked locus responsible for red-green color blindness.Three alleles of this SSLP are known: "4 repeats," "5 repeats," and "7 repeats." A woman with normal color vision,but whose father is color blind,marries a man with normal vision,and they have a son. $\begin{array}{|l|l|l|l}\hline \begin{array}{l}\text { Family } \\\text { member }\end{array} & \text { SSLP genotype } & \text { Family member } & \text { SSLP genotype } \\\hline \begin{array}{l}\text { Woman's } \\\text { father }\end{array} & \text { "5 repeats" } & \text { Woman's husband } & \text { "3 repeats" } \\\hline \text { Woman } & \begin{array}{l}\text { "5 repeats"/"7 } \\\text { repeats" }\end{array} & \text { Couple's child } & \text { "5 repeats" }\\\hline \end{array}$
Given the SSLP genotypes of the family members shown above,what is the probability that the couple's son is color blind?

A)2%
B)50%
C)98%
D)99%
E)100%

Question 34

In unordered tetrad analyses of two linked loci,a nonparental ditype is an indication of:

A)no crossovers.
B)single crossover.
C)two chromatid double crossover.
D)three chromatid double crossover.
E)four chromatid double crossover.

Question 35

In a dihybrid female fruit fly with genotype AaBb,88% of the meiosis there are no chiasmata between the A and B loci,and in 12% there is one.What is the expected frequency of recombinant gametes produced by this fly?

A)3%
B)6%
C)12%
D)24%
E)50%

Question 36

Dihybrid AaBb female Drosophila were testcrossed with aabb males.The following offspring genotypes were obtained.
AaBb $\quad$ 99
Aabb $\quad$ 83
AaBb $\quad$ 86
Aabb $\quad$ 92
A $\chi$ ² test was performed to determine whether the data supported the original hypothesis that the genes are unlinked.What is the correct value of $\chi$ ²?

A)0.24
B)0.42
C)0.47
D)1.67
E)2.79

Question 37

In Neurospora,a,b,and c are auxotrophic mutants (require particular compounds for growth).The mating a b⁺ *a⁺b gives 5% prototrophs (grown on unsupplemented medium).The mating b⁺c * b c⁺ gives 2.5% prototrophs,and the mating a⁺c * a c⁺ gives 2.5% prototrophs.Assuming complete interference prevails in the chromosome segment in question,what percent of prototrophs would you expect in the mating a⁺b c⁺ * a b⁺c? (The order of mutations is not necessarily a,b,c: It can be determined on the basis of the two-point crosses above.)

A)0%
B)0.0625%
C)0.125%
D)2.5%
E)5%

Question 38

Neurospora loci d and f are located on the same chromosome.The d locus always segregates at M_I,while the e locus segregates at M_II at a frequency of 10%.Assuming complete interference,the expected frequency of parental ditypes in the progeny of a cross d⁺e⁺ $\times$ d e is:

A)30%.
B)40%.
C)45%.
D)80%.
E)90%.

Question 39

A dihybrid AaBb female Drosophila is testcrossed with an aabb male.The following offspring genotypes were obtained.
AaBb $\quad$ 99
Aabb $\quad$ 83
AaBb $\quad$ 86
Aabb $\quad$ 92
A $\chi$ ² test was performed to determine whether the data supported the original hypothesis that the genes are unlinked.How many degrees of freedom should be used in this analysis?

A)1
B)2
C)3
D)4
E)5

Question 40

In the cross mt⁺al⁺ $\times$ mt al,the mt locus shows an M_II frequency of 12%,the al locus an M_II frequency of 10%.Most asci were parental ditypes.The order of loci is:

A)al - centromere - mt.
B)al - mt - centromere.
C)centromere - al - mt.
D)centromere - mt - al.
E)mt - centromere - al.

Question 41

In the following cross,the genes are inherited independently except for C and D,which are tightly linked and show zero recombination: A/A ;b/b ;c/c ;D/D ;e/e ;F/F - a/a ;B/B ;C/C ;d/d ;E/E ;f/f.In the F₂,what proportion of individuals will be:
a)pure breeding?
b)heterozygous for all loci?
c)homozygous recessive for all loci?
d)A/a;B/B;c/c;D/D;E/e;f/f?
e)phenotypically like either parent?
f)phenotypically unlike either parent?
g)genotypically like either parent?
h)genotypically unlike either parent?

Question 42

An experiment was done to determine the linkage relationship of three genes (a,b,and c)in Drosophila melanogaster.Homozygous females phenotypically a,c were crossed with homozygous males phenotypically b.The F₁ females were all wild type in appearance,and the F₁ males were all a,c.The F₁ females and males were crossed to give the following F₂ phenotypes and numbers.
$\quad$ $\quad$ $\quad$ $\quad$ $\quad$$\text { Number of }$
$\begin{array}{|c|c|c|}\hline &\text { Males } & \text { Females }\\\hline a+c & 242 & 310 \\\hline+b+ & 238 & 0 \\\hline a b+ & 157 & 0 \\\hline++c & 163 & 190 \\\hline a b c & 59 & 0 \\\hline+++ & 61 & 295 \\\hline a++ & 38 & 205 \\\hline+b c & 42 & 0 \\\hline \text { Total } & 1,000 & 1,000 \\\hline\end{array}$
a)Give the genotypes of the parents.
b)Give the genotypes of the F₁ flies,and show the genotypic arrangement in the female F₁.
c)Draw a genetic map showing the order of the genes and the distances between them.
d)Calculate the interference (only if necessary;if not,say "I = 0").

Question 43

The fungal cross a ^. b⁺ $\times$ a^{+ .} b yields 30 parental ditype,27 nonparental ditype,and 18 tetratype asci.The two genes,a and b,are:

A)linked,36 map units apart (the RF being 36%).
B)linked,45 map units apart (the RF being 45%).
C)unlinked,90 map units apart (the RF being 45%).
D)unlinked,96 map units apart (the RF being 48%).
E)unlinked,over 100 map units apart (the RF being 48%).

Question 44

A cross was made between two Neurospora strains with genotypes + b and a +.The genes are linked.The genotypes of the spores in one ascus from this cross are listed in order,from left to right:
$$+ b ; + b ; + + ; + + ; a b ; a b ; a + ; a +$$
a)Is the ascus a parental ditype (PD),a tetratype (T),or a nonparental ditype (NPD)?
b)Do the alleles of the a gene show first or second division segregation?
c)Do the alleles of the b gene show first or second division segregation?
d)Show how the above tetrad of spore pairs was derived by diagramming the chromosomes at pachytene of meiosis I.Indicate with a line between appropriate chromatids,the simplest crossover that can yield this tetrad.
e)If recombination between a and b is 10% and 2/100 asci are NPD,how many tetratype asci would you expect to find? How many PD?
f)Diagram how a tetrad with the same spore pairs,as shown above,would arise if the genes showed independent assortment.

Question 45

In one short chromosome arm the average frequency of crossovers per meiosis was measured to be 0.5.What proportion of meioses will have no crossovers at all in this region?

A)0.40
B)0.52
C)0.60
D)0.74
E)0.90

Question 46

Two albino strains of Neurospora are crossed.Of 200 progeny,195 are albino and 5 are wild type (orange).Each parent,when mated with wild type,gives 1/2 wild-type and 1/2 albino progeny.
a)How can you tell that the two mutations involved here represent different genes?
b)What is your best estimate of map distance between the two mutations and how did you calculate it?

Question 47

A fruit fly of genotype a⁺/a ^. b⁺/b (parent 1)is crossed to another fruit fly of genotype a/a ^. b/b (parent 2).The progeny of this cross were:
$$\begin{array} { l l } \text { Genotype } & \text { Number of individuals } \\\hline a ^ { + } / a \cdot b ^ { + }/ b & 38 \\a / a \cdot b / b & 37 \\a ^ { + } / a \cdot b / b & 12 \\a / a \cdot b ^ { + } / b & 13\end{array}$$
a)What gametes were produced by parent 1 and in what proportions?
b)Do these proportions demonstrate independent assortment of the two genes?
c)What can be deduced from these proportions?
d)Demonstrate the arrangement of the genes on the chromosomes in parents 1 and 2 using the appropriate symbols.
e)Draw a diagram or diagrams to explain the origin of the two rarest progeny genotypes.

Question 48

Four possibly different albino strains of Neurospora were each crossed to wild type.All crosses resulted in 1/2 wild-type and 1/2 albino progeny.Crosses were made between the first strain and the other three with the following results:
1 $\times$ 2: 975 albino : 25 wild type
1 $\times$ 3: 1000 albino
1 $\times$ 4: 750 albino : 250 wild type
Which mutations represent different genes and which genes are linked? How did you arrive at your conclusions?

Question 49

The molecular process which results in the formation of recombinant chromosomes is initiated by:

A)a single-stranded break in one of the chromatids.
B)a double-stranded break in one of the chromatids.
C)the formation of heteroduplex DNA.
D)the invasion of single-stranded DNA.
E)a Holliday junction.

Question 50

In a cross between an arginine-requiring,acetate-requiring strain of Neurospora and a wild-type strain (arg ac * + +)the following ordered tetrads of asci were found,with the numbers of each type indicated below the particular tetrad:


a)Calculate the map distance between arg and its centromere.
b)Calculate the map distance between ac and its centromere.
c)What is the most likely map of the two genes in relation to each other and to the position of their respective centromere(s)?

Question 51

Using data from a testcross of a dihybrid,a $\chi$ ² value of 6.5 was obtained,with 3 degrees of freedom.What is the correct interpretation of this result?

A)The p value is approximately 0.01 (1%),so the hypothesis of no linkage should be rejected.
B)The p value is approximately 0.01 (1%),so the hypothesis of no linkage should not be rejected.
C)The p value is approximately 0.1 (10%),so the hypothesis of no linkage should be rejected.
D)The p value is approximately 0.1 (10%),so the hypothesis of no linkage should not be rejected.

Question 52

In a cross in which there is a mean crossover frequency of 0.9 between two marker loci,the recombinant frequency for those loci will be:

A)5%.
B)10%.
C)30%.
D)45%.
E)90%.

Question 53

Three crosses involving three linked genes were performed,with the resulting "shorthand" designation of phenotypes indicated:


What is the best map of these three genes?

Question 54

Which of the following is one of the steps that occurs during the process of crossing over?

A)mitosis
B)meiosis
C)translation
D)transcription
E)replication

Question 55

Draw a linkage map or maps consistent with the following recombination frequencies:
a)A-B 30%,A-C 50%,B-C 50%,B-D 50%,A-D 50%,C-D 15%
b)A-B 30%,A-C 50%,B-C 20%,B-D 35%,A-D 50%,C-D 15%

Question 56

In a fungal cross of A B X a b (the loci are linked)in meiosis in which there has been a four-strand double crossover between the loci,the percent of meiotic products that will be recombinant for A and B for that ascus is:

A)0.
B)25.
C)50.
D)75.
E)100.

Question 57

In Neurospora,an Irish strain makes big as well as green-colored colonies (genotype b g).It is crossed to a wild-type strain,which makes small and orange-colored colonies (genotype: + +).The following ordered tetrads of asci were found,with the numbers of each type indicated below each tetrad.
$$\begin{array} { l l l l l l l } \text { I}& \text { II } & \text { III } & \text { IV } & \text { V } & \text { VI } & \text { VII } \\b g & b + & b g & b g & b g & b + & b g \\+ + & + g & + + & + g & b + & b + & b g \\+ g & b + & b g & b + & + g & + g & + + \\b + & + g & + + & + + & + + & + g & + + \\\hline 4 & 1& 24 & 1 & 91 & 2 & 177\end{array}$$
a)Classify the asci above (I-VII)according to type.
(i) those which are PD
(ii) those which are NPD
(iii) those which are $\mathrm{T}$

b)Calculate the percent recombination between b and its centromere.
c)Calculate the percent recombination between g and its centromere.
d)What is the most likely map of the two genes in relation to each other and to the position of their respective centromere(s)?

Question 58

In humans,the allele N causes an abnormal shape of the patella in the knee (n is the normal allele).A separate gene is concerned with finger length,and the allele B causes abnormally short fingers,whereas b gives normal length.A study focused on people who have both abnormal patellae and short fingers (they were most likely N/n ^. B/b in genotype),having inherited the N allele from one parent and the B allele from the other parent.These N/n ^. B/b people mated with normal spouses,producing 40 progeny classified as follows:
$$\begin{array} { l l } \text { Normal } & 3 \\\text { Abnomal knees and fingers } & 2 \\\text { Abromal knees only } & 17 \\\text { Abnomal fingers only } & 18\end{array}$$
a)Draw the chromosomes of the N/n ^. B/b individuals,their parents,and their four types of children,showing the positions of the alleles.
b)Explain why the four types of children were in the proportions shown.

Question 59

Three genes of corn,R,D,and Y,lie on chromosome 9.The map of the three genes,using map units is as follows:
$$\begin{array} { l l l l l } R & 10 & D& 5 & Y \\\hline\end{array}$$
In a testcross of a trihybrid plant (R D Y/r d y)arising from true-breeding R D Y/R D Y and r d y/r d y parents,how many R d Y/- d - plants would be expected in a progeny of 1000 if there were no interference? If the coefficient of coincidence were 0.3,how would this change your answer?

Question 60

Holliday junctions are:

A)formed during the process of crossing over.
B)the end products of the process of crossing over.
C)a type of mismatched DNA.
D)a type of mutation.
E)a type of heteroduplex DNA.

Question 61

Dominant alleles at two different loci affect the tail of mice.These genes are linked and both are lethal in the embryo when homozygous.One of the tail genes is called brachyury (T),and these mice have short tails.A third gene,histocompatibility-2 (H-2),is linked to the tail genes and is concerned with tissue transplantation.Mice that are H-2/+ will accept tissue grafts,unlike +/+.A cross was carried out between male T H-2/ + + and female + +/+ + mice,and produced the following baby mice.
$$\begin{array} { l l } \text { Brachy tail, accepts graft } & 105 \\\text { Narmal tail, rejects graft } & 115 \\\text { Brachy tail, rejects graft } & 14 \\\text { Narmal tail, accepts graft } & \underline {1 6 }\\&250\end{array}$$
Determine if the linkage between H-2 and T is significant using the chi-square test.

Question 62

Consider the following experimental results.
(M = mapping function and MU = M x 50)
$$\begin{array} { c c c } \text { OBSERVED RF } & \mathrm { M } & \mathrm { MU } \\18.5 \% & 0.46 & 23.1 \\& & \\6.4 \% & 0.137 & 6.8\end{array}$$
Based on these results,would you advocate the use of mapping functions? In which situations would you recommend using them?

Question 63

In a fungal cross $a b * + +$ ,gene a is on chromosome 1 and gene b is on chromosome 6.It is known that the two loci are so closely linked to their centromeres that there is never any crossing over in either centromere to locus region.What proportion of linear tetrads will be:
a)M_I M_I PD?
b)M_I M_I NPD?
c)M_I M_II T?
d)M_II M_I T?
e)M_II M_II PD?
f)M_II M_II NPD?
g)M_II M_II T?

Question 64

In the fungus Neurospora,a strain that was auxotrophic for thiamine (mutant allele t)was crossed to a strain that was auxotrophic for methionine (mutant allele m).Linear asci were isolated,and they were classified in the following groups:


a)Determine the linkage relationships of these two genes to their centromere(s)and to each other.Specify distances in map units.

b)If 1000 randomly selected ascospores are plated on a plate of minimal medium,how many are expected to grow into colonies?