Genetics: A Conceptual Approach

Benjamin Pierce

Chapter 7 Linkage, Recombination, and Eukaryotic Gene Mapping - all with Video Answers

Educators

+ 1 more educators

Chapter Questions

03:16

Problem 1

What does the term recombination mean? What are two causes of recombination?

Mariana Roldan

Numerade Educator

03:01

Problem 2

In a testcross for two genes, what types of gametes are produced with (a) complete linkage, (b) independent assortment, and (c) incomplete linkage?

Mariana Roldan

Numerade Educator

01:37

Problem 3

What effect does crossing over have on linkage?

Mariana Roldan

Numerade Educator

02:57

Problem 4

Why is the frequency of recombinant gametes always half the frequency of crossing over?

Mariana Roldan

Numerade Educator

03:08

What is the difference between genes in coupling configuration and genes in repulsion? How does the arrangement of linked genes (whether they are in coupling or repulsion) affect the results of a genetic cross?

Mariana Roldan

Numerade Educator

01:32

Problem 6

How would you test to see if two genes are linked?

Mariana Roldan

Numerade Educator

01:36

Problem 7

What is the difference between a genetic map and a physical map?

Rabeya Zahid

Numerade Educator

02:07

Problem 8

Why do calculated recombination frequencies between pairs of loci that are located far apart underestimate the true genetic distances between loci?

Mariana Roldan

Numerade Educator

02:50

Problem 9

Explain how to determine, using the numbers of progeny from a three-point cross, which of three linked loci is the middle locus.

Mariana Roldan

Numerade Educator

02:54

Problem 10

What does the interference tell us about the effect of one crossover on another?

Mariana Roldan

Numerade Educator

03:04

Problem 11

What is a lod score and how is it calculated?

Mariana Roldan

Numerade Educator

07:01

Problem 12

List some of the methods for physically mapping genes and explain how they are used to position genes on chromosomes.

Mariana Roldan

Numerade Educator

View

Problem 13

The introduction to this chapter described the search for genes that determine pattern baldness in humans. In $1916,$ Dorothy Osborn suggested that pattern baldness is a sex-influenced trait (see Chapter 5 ) that is dominant in males and recessive in females. More research suggested that pattern baldness is an X-linked recessive trait. Would you expect to see independent assortment between genetic markers on the X chromosome and pattern baldness if (a) pattern baldness is sex-influenced and (b) if pattern baldness is X-linked recessive? Explain your answer.

Andrei Demkov

Numerade Educator

10:45

Problem 14

In the snail Cepaea nemoralis, an autosomal allele causing a banded shell $\left(B^{\text {st }}\right)$ is recessive to the allele for an unbanded shell $\left(B^{\circ}\right)$. Genes at a different locus determine the backg round color of the shell; here, yellow $\left(C^{Y}\right)$ is recessive to brown $\left(C^{\theta_{m}}\right) .$ A banded, yellow snail is crossed with a homozygous brown, unbanded snail. The $F_{1}$ are then crossed with banded, yellow snails (a testcross).
a. What will the results of the testcross be if the loci that control banding and color are linked with no crossing cover?
b. What will the results of the testcross be if the loci assort independently?
c. What will the results of the testcross be if the loci are linked and 20 m.u. apart?

Sana Riaz

Numerade Educator

07:18

Problem 15

In silkmoths (Bombyx mori), red eyes (re) and whitebanded wing $(w b)$ are encoded by two mutant alleles that are recessive to those that produce wild-type traits $\left(r e^{+} \text {and } w b^{+}\right) ;$ these two genes are on the same chromosome. A moth homozygous for red eyes and white-banded wings is crossed with a moth homozygous for the wild-type traits. The $F_{1}$ have normal eyes and normal wings. The $\mathrm{F}_{1}$ are crossed with moths that have red eyes and white-banded wings in a testcross. The progeny of this testcross are: wild-type eyes, wild-type wings red eyes, wild-type wings wild-type eyes, white-banded wings red eyes, white-banded wings 418
19
16
426

Sana Riaz

Numerade Educator

04:00

Problem 16

A geneticist discovers a new mutation in Drosophila melanogaster that causes the flies to shake and quiver. She calls this mutation spastic ( $s p s$ ) and determines that it is due to an autosomal recessive gene. She wants to determine whether the gene encoding spastic is linked to the recessive gene for vestigial wings $(v g) .$ She crosses a fly homozygous for spastic and vest ig ial traits with a fly homozygous for the wild-type traits and then uses the resulting $\mathrm{F}_{1}$ females in a testcross. She obtains the following flies from this testcross. (TABLE CANNOT COPY) Are the genes that cause vestigial wings and the spastic mutation linked? Do a chi-square test of independence to determine whether the genes have assorted independently.

Sana Riaz

Numerade Educator

05:12

Problem 17

In cucumbers, heart-shaped leaves $(h l)$ are recessive to normal leaves $(H I)$ and having numerous fruit spines $(n s)$ is recessive to having few fruit spines $(N s) .$ The genes for leaf shape and for number of spines are located on the same chromosome; findings from mapping experiments indicate that they are 32.6 m.u. apart. A cucumber plant having heart-shaped leaves and numerous spines is crossed with a plant that is homozygous for normal leaves and few spines. The $F_{1}$ are crossed with plants that have heart-shaped leaves and numerous spines. What phenotypes and phenotypic proportions are expected in the progeny of this cross?

Caroline Jones

Numerade Educator

02:52

Problem 18

In tomat oes, tall $(D)$ is dominant over dwarf $(d)$ and smooth fruit $(P)$ is dominant over pubescent fruit $(p)$ which is covered with fine hairs. A farmer has two tall and smooth tomato plants, which we will call plant A and plant $B$. The farmer crosses plants $A$ and $B$ with the same dwarf and pubescent plant and obtains the following numbers of progeny: (EQUATION CANNOT COPY)
a. What are the genotypes of plant A and plant B?
b. Are the loci that determine the height of the plant and pubescence linked? If so, what is the percent recombinat ion between them?
c. Explain why different proportions of progeny are produced when plant $A$ and plant $B$ are crossed with the same dwarf pubes cent plant.

Sana Riaz

Numerade Educator

07:24

Problem 19

Alleles $A$ and $a$ are at a locus on the same chromosome as is a locus with alleles $B$ and $b$. Aa $B b$ is crossed with aa bb and the following progeny are produced: $$\begin{array}{lr}\text {Aa Bb} & 5 \\\text {Aa bb} & 45 \\\text {aa Bb} & 45 \\ \text {aa bb} & 5\end{array}$$
What condusion can be made about the arrangement of the genes on the chromosome in the Aa $B b$ parent?

Sana Riaz

Numerade Educator

05:56

Problem 20

Daniel McDonald and Nancy Peer determined that eye spot (clear spot in the center of the eye) in flour beetles is caused by an X-linked gene $(e s)$ that is recessive to the allele for the absence of eye spot $\left(e s^{+}\right)$ They conducted a series of crosses to determine the distance between the gene for eye spot and a dominant X-linked gene for striped $(S t),$ which causes white stripes on females and acts as a recessive lethal (is lethal when homozygous in females or hemizygous in males). The following cross was carried out (D. J. McDonald and N. J. Peer. $1961 .$ Journal of Heredity $52: 261-264$ ).
(EQUATION CANNOT COPY)
a. Which progeny are the recombinants and which progeny are the nonrecombinants?
b. Calculate the recombination frequency between $e s$ and $S t$
c. Are some potential genotypes missing among the progeny of the cross? If so, which ones and why?

Bryan Lynn

Numerade Educator

01:43

Problem 21

Recombination rates between three loci in corn are shown here. $\begin{array}{cc}\text { Loci } & \text { Recombination rate } \\ R \text { and } W_{2} & 17 \% \\ R \text { and } L_{2} & 35 \% \\ W_{2} \text { and } L_{2} & 18 \%\end{array}$What is the order of the genes on the chromosome?

Sana Riaz

Numerade Educator

03:24

Problem 22

In tomatoes, dwarf $(d)$ is recessive to tall $(D)$ and opaque (light-green) leaves $(o p)$ are recessive to green leaves $(O p) .$ The loci that determine height and leaf color are linked and separated by a distance of 7 m.u. For each of the following crosses, determine the phenotypes and proportions of progeny produced.
a. $\frac{D}{d} \frac{O p}{o p} \times \frac{d}{d} o p$
b. $\frac{D}{d} \frac{o p}{O p} \times \frac{d}{d} \quad o p$
c. $\frac{D}{d} \frac{O p}{o p} \times \frac{D}{d} \frac{O p}{o p}$
d. $\frac{D}{d} \frac{o p}{O p} \times \frac{D}{d} \quad o p$

Sana Riaz

Numerade Educator

07:37

Problem 23

In German cockroaches, bulging eyes $(b u)$ are recessive to normal eyes $\left(b u^{+}\right)$ and curved wings $(c v)$ are recessive to straight wings $\left(c v^{+}\right) .$ Both traits are encoded by autosomal genes that are linked. A cockroach has genotype $b u^{+} b u c v^{+} c v,$ and the genes are in replusion. Which of the following sets of genes will be found in the most-common gametes produced by this cockroach?
a. $b u^{+} c v^{+}$
b. bu c $v$
c. $b u^{+} b u$
d. $c v^{+} c v$
e. bu $c v^{+}$
Explain your answer.

Sana Riaz

Numerade Educator

02:26

Problem 24

In Drosophila mdanogaster, ebony body ( $e$ ) and rough eyes $(r o)$ are encoded by autosomal recessive genes found on chromosome $3 ;$ they are separated by 20 m.u. The gene that encodes forked bristles $(f)$ is $X$ -linked recessive and assorts independently of $e$ and ro. Give the phenotypes of progeny and their expected proportions when a female of each of the following genotypes is test-crossed with a male. a. $\frac{e^{+}}{e} \quad \frac{r o^{+}}{r o} \quad \frac{f^{+}}{f}$
$\mathbf{b} \cdot \frac{e^{+}}{e} \frac{m}{r o^{+}} \frac{f^{+}}{f}$

Sana Riaz

Numerade Educator

04:54

Problem 25

Honeybees have haplodiploid sex determination: females are diploid, developing from fertilized eggs, whereas males are haploid, developing from unfertilized eggs. Otto Mackensen studied linkage relations among eight mutations in honeybees (O. Mackensen. 1958. Journal of Heredity $49: 99-102$ ). The following table gives the results of two of MacKensen's crosses induding three recessive mutations: $c d$ (condovan body color), $h$ (hairless), and $c h$ (chartreuse eye color).
Queen genotype
$$\begin{array}{cc}c d & h^{+} \\\hline c d^{+} & h \\h & c h^{+} \\\hline h^{+} & c h\end{array}$$
Phenotypes of drone (male) progeny
294 cordovan, 236 hairless, 262 cordovan and hairless, 289 wild type
3131 hairless, 3064 chartreuse, 96 chartreuse and hairless, 132 wild type
a. Only the genotype of the queen is given. Why is the genotype of the male parent not needed for mapping these genes? Would the genotype of the male parent be required if we examined female progeny instead of male progeny?
b. Determine the nonrecombinant and recombinant progeny for each cross and calculate the map distances between $c d, h,$ and $c h .$ Draw a linkage map illustrating the linkage arrangements among these three genes.

Sana Riaz

Numerade Educator

01:50

Problem 26

Perform a chi-square test of independence on the data provided in Figure 7.2 to determine if the genes for flower color and pollen shape in sweet peas are assorting independently. Give the chi-square value, degrees of freedom, and associated probability. What conclusion would you make about the independent assor tment of these genes?

Sheryl Ezze

Numerade Educator

08:43

Problem 27

A series of two-point crosses were carried out among seven loci $(a, b, c, d, e, f, \text { and } g),$ producing the following recombination frequencies. Map the seven loci, showing their linkage groups, the order of the loci in each linkage group, and the distances between the loci of each group.(TABLE CANNOT COPY)

Rashmi Sinha

Numerade Educator

06:39

Problem 28

R. W. Allard and W. M. Clement determined recombination rates for a series of genes in lima beans (R. W. Allard and W. M. Clement. 1959. Journal of Heredity $50: 63-67$ ). The following table lists paired recombination rates for eight of the loci $\left(D, W l, R, S, L_{1}, M s, C, \text { and } G\right)$ that they mapped. On the basis of these data, draw a series of genetic maps for the different linkage groups of the genes, indicating the distances between the genes. Keep in mind that these rates are estimates of the true recombination rates and that some error is associated with each estimate. An asterisk beside a recombination frequency indicates that the recombination frequency is significantly different from $50 \%$ (TABLE CANNOT COPY)

Rashmi Sinha

Numerade Educator

05:04

Problem 29

Raymond Popp studied linkage among genes for pink eye $(p),$ shaker-1 $(s h-1,$ which causes circling behavior, head tossing, and deafness), and hemoglobin $(H b)$ in mice (R. A. Popp. 1962. Journal of Heredity 53:73-80). He perfor med a series of testcrosses, in which mice heterozygous for pink eye, shaker-1, and hemoglobin 1 and 2 were crossed with mice that were homozygous for pink eye, shaker- $1,$ and hemoglobin 2 $$\frac{P S h-1 H b^{1}}{p s h-1 H b^{2}} \times \frac{p s h-1 H b^{2}}{p s h-1 H b^{2}}$$ The following progeny were produced. (TABLE CANNOT COPY)
a. Determine the order of these genes on the chromosome.
b. Calculate the map distances between the genes.
c. Determine the coefficient of coincidence and the interference among these genes.

Sana Riaz

Numerade Educator

04:30

Problem 30

Waxy endosperm $(w x),$ shrunken endosperm $(s h),$ and yellow seedling $(v)$ are encoded by three recessive genes in corn that are linked on chromosome $5 .$ A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting $\mathrm{F}_{1}$ are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are: (TABLE CANNOT COPY)
a. Determine the order of these genes on the chromosome.
b. Calculate the map distances between the genes.
c. Determine the coefficient of coincidence and the interference among these genes.

Sana Riaz

Numerade Educator

05:13

Problem 31

Priscilla Lane and Margaret Green studied the linkage relations of three genes affecting coat color in mice: mahogany $(m g),$ agouti $(a),$ and ragged $(R g) .$ They carried out a series of three-point crosses, mating mice that were heterozygous at all three loci with mice that were homozygous for the recessive alleles at these loci (P W. Lane and M. C. Green. 1960. Journal of Heredity $51: 228-230) .$ The following table lists the results of the testcrosses.
(TABLE CANNOT COPY)
a. Determine the order of the loci that encode mahogany, agouti, and ragged on the chromosome, the map distances between them, and the interference and coefficient of coincidence for these genes.
b. Draw a picture of the two chromosomes in the triply heterozygous mice used in the testcrosses, indicating which of the alleles are present on each aosome

Sana Riaz

Numerade Educator

10:50

Problem 32

Fine spines $(s),$ smooth fruit $(t u),$ and uniform fruit color $(u)$ are three recessive traits in cucumbers, the genes of which are linked on the same chromosome. A cucumber plant heterozygous for all three traits is used in a testcross, and the following progeny are produced from this testcross: (TABLE CANNOT COPY)
a. Determine the onder of these genes on the chromosome.
b. Calculate the map distances between the genes.
c. Determine the coefficient of coincidence and the interference among these genes.
d. List the genes found on each chromosome in the parents used in the testcross.

Bryan Lynn

Numerade Educator

06:35

Problem 33

In Drosophila melanogaster, black body $(b)$ is recessive to gray body $\left(b^{+}\right),$ purple eyes $(p r)$ are recessive to red eyes $\left(p r^{+}\right),$ and vestigial wings $(v g)$ are recessive to normal wings $\left(v g^{+}\right) .$ The loci encoding these traits are linked, with the following map distances: (FIGURE CANNOT COPY) The interference among these genes is $0.5 .$ A fly with a black body, purple eyes, and vestigial wings is crossed with a fly homozygous for a gray body, red eyes, and normal wings. The female progeny are then crossed with males that have a black body, purple eyes, and vestigial wings. If 1000 progeny are produced from this testcross, what will be the phenotypes and proportions of the progeny?

Caroline Jones

Numerade Educator

03:26

Problem 34

Sepia eyes, spineless bristles, and striped thorax are three recessive mutations in Drosophila found on chromosome $3 .$ A genetics student crosses a fly homozygous for sepia eyes, spineless bristles, and striped thorax with a fly homozygous for the wild-type traits - red eyes, normal bristles, and solid thorax. The female progeny are then testcrossed with males that have sepia eyes, spineless bristles, and striped thorax. Assume that the interference between these genes is 0.2 and that 400 progeny flies are produced from the test cross. Based on the map distances provided in Figure 7.15 predict the phenotypes and proportions of the progeny resulting from the test cross.

Sana Riaz

Numerade Educator

06:40

Problem 35

Shown below are eight DNA sequences from different individuals.
(FIGURE CANNOT COPY)
a. Give the nucleotide positions of all single nucleotide polymorphisms (SNPs; nucleotide positions where individuals vary in which base is present ) in these sequences.
b. How many different haplotypes (sets of linked variants) are found in these eight sequences?
c. Give the haplotype of each sequence by listing the specific bases at each variable position in that particular haplotype. (Hint: See Figure 20.8)

Sana Riaz

Numerade Educator

02:47

Problem 36

A group of geneticists are interested in identifying genes that may play a role in susceptibility to asthma. They study the inheritance of genetic markers in a series of families that have two or more asthmatic children. They find an association between the presence or absence of asthma and a genetic marker on the short arm of chromosome 20 and calculate a lod score of 2 for this association. What does this lod score indicate about genes that may influence asthma?

Mariana Roldan

Numerade Educator

02:55

Problem 37

A panel of cell lines was created from human-mouse somatic-cell fusions. Each line was examined for the presence of human chromosomes and for the production of an enzyme. The following results were obtained: (FIGURE CANNOT COPY)On the basis of these results, which chromosome has the gene that encodes the enzyme?

Christopher Starmer

Numerade Educator

01:20

Problem 38

A panel of cell lines was created from human-mouse somatic-cell fusions. Each line was examined for the presence of human chromosomes and for the production of three enzymes. The following results were obtained. (FIGURE CANNOT COPY) On the basis of these results, give the chromosome location of enzyme $1,$ enzyme $2,$ and enzyme 3

Rabeya Zahid

Numerade Educator

01:24

Problem 39

The locations of six deletions have been mapped to the Drosophila chromosome, as shown in the following deletion map. Recessive mutations $a, b, c, d, e,$ and $f$ are known to be located in the same region as the deletions, but the order of the mutations on the chromosome is not known. (FIGURE CANNOT COPY) When flies homozygous for the recessive mutations are crossed with flies homozygous for the deletions, the following results are obtained, in which "m" represents a mutant phenotype and a plus sign ( $+)$ represents the wild type. On the basis of these data, determine the relative order of the seven mutant genes on the chromosome: (TABLE CANNOT COPY)

Rabeya Zahid

Numerade Educator

01:47

Problem 40

Transferrin is a blood protein that is encoded by the tran sferrin locus (Trf). In house mice, the two alleles at this locus $(\text { Trf }^{\text {t }} \text { and } \text {Trf}^{\text {b }}$ ) are codominant and encode three types of transferrin:
(TABLE CANNOT COPY) The dilution locus, found on the same chromosome, determines whether the color of a mouse is diluted or full; an allele for dilution $(d)$ is recessive to an allele for full color $\left(d^{7}\right):$ (TABLE CANNOT COPY) Donald Shreffler conducted a series of crosses to determine the map distance between the tranferrin locus and the dilution locus (D. C. Shreffler. 1963. Journal of Heredity $54: 127-129)$. The following table presents a series of crosses carried out by Shreffler and the progeny resulting from these crosses. (TABLE CANNOT COPY)
a. Calculate the recombination frequency between the Trf and the $d$ loci by using the pooled data from all the crosses.
b. Which crosses represent recombination in male gamete formation and which crosses represent recombination in female gamete formation?
c. On the basis of your answer to part $b$, calculate the frequency of recombination among male parents and female parents separately.
d. Are the rates of recombination in males and females the same? If not, what might produce the difference?

Sana Riaz

Numerade Educator

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7

Problem 8

Problem 9

Problem 10

Problem 11

Problem 12

Problem 13

Problem 14

Problem 15

Problem 16

Problem 17

Problem 18

Problem 19

Problem 20

Problem 21

Problem 22

Problem 23

Problem 24

Problem 25

Problem 26

Problem 27

Problem 28

Problem 29

Problem 30

Problem 31

Problem 32

Problem 33

Problem 34

Problem 35

Problem 36

Problem 37

Problem 38

Problem 39

Problem 40