Deck 6: Gene Interaction

Question 1

In the purple penguin,an allelic series occurs at the p locus on an autosome.All alleles affect the color of feathers: p^d = dark-purple,p^m = medium-purple,p^l = light-purple,and p^vl = very pale purple.The order of dominance is p^d > p^m > p^l > p^vl.If a p^l/p^vl female is crossed to a p^d/p^mmale,the ratio of phenotypes expected among the baby penguins would be:

A)2 dark:1 light:1 very pale.
B)2 dark:1 medium:1 light.
C)1 dark:1 medium.
D)1 dark:1 medium:1 light:1 very pale.
E)1 medium:1 light.

Answer 1

C

Question 2

Two new mutant lines of a flowering plant have been obtained; one breeds true for blue flower color and the other breeds true for red flower color (wild-type flower color is purple). Consider the following crosses.
1. blue $\times$ purple $\rightarrow \mathrm { F } _ { 1 }$ all purple $\rightarrow \mathrm { F } _ { 2 } 75 \%$ purple; $25 \%$ blue
2. red $\times$ purple $\rightarrow \mathrm { F } _ { 1 }$ all purple $\rightarrow \mathrm { F } _ { 2 } 75 \%$ purple; $25 \%$ red
3. red $\times$ blue $\rightarrow \mathrm { F } _ { 1 }$ all purple

If the purple flower color results from the mixture of red and blue pigments,and all the intermediate products in the pigment pathways are colorless,what phenotypic ratios do you expect in the F₂ of cross 3?

A)3 purple : 1 white (colorless)
B)9 purple : 3 blue : 3 red : 1 white (colorless)
C)9 purple : 4 blue : 3 red
D)9 purple : 7 white (colorless)
E)12 purple : 3 blue : 1 white (colorless)

Answer 2

9 purple : 3 blue : 3 red : 1 white (colorless)

Question 3

In a wild-type fungus,protein E (encoded by the haplosufficient gene "E")normally homodimerizes,and the E-E dimer catalyzes a biochemical reaction necessary for the production of a dark pigment.E^D represents a mutant,dominant,negative allele of gene E.What is the predicted phenotype of a fungus cell of genotype E⁺/E^D,and why?

A)mutant (no pigment production),as E is haplosufficient
B)mutant (no pigment production),as no E-E dimers will form in the heterozygous
C)mutant (no pigment production),as the mutant allele E^D is dominant
D)wild type (normal production of the dark pigment),as E^D is a negative allele
E)wild type (normal production of the dark pigment),as E is haplosufficient

Answer 3

C

Question 4

Remember that,in Labrador retrievers,B (black coat)is dominant to b (brown coat)and homozygosity for the recessive epistatic allele e always results in a yellow coat.A brown female is crossed to a yellow male,and their progeny consists of six black puppies.Interestingly,when one of the F₁ females is crossed to her yellow father,she gives birth to seven puppies: three yellow,three black,and one brown. What are the most likely genotypes of the original brown female and yellow male?

A)b/b;E/E (female)and B/B;e/e (male)
B)b/b;E/E (female)and B/b;e/e (male)
C)b/b;E/e(female)and B/B;e/e (male)
D)b/b;E/e(female)and B/b;e/e (male)
E)b/b;E/E (female)and b/b;e/e (male)

Question 5

In laboratory mice,the "short tail" phenotype is dominant to the wild-type ("long tail")phenotype.However,crosses between any two short-tailed mice always produce mixtures of short- and long-tailed offspring.Assuming that tail length is controlled by a single locus,a likely explanation for these results is that the "short tail" allele is:

A)a codominant allele.
B)a dominant lethal allele.
C)haploinsufficient.
D)an incompletely dominant allele.
E)a recessive lethal allele.

Question 6

In the multiple-allele series that determines coat color in rabbits,c⁺ encodes agouti,c^ch encodes chinchilla,and c^h encodes Himalayan.Dominance within this allelic series is c⁺>c^ch > c^h.In a cross of c⁺/c^h $\times$ c^ch/c^h,what proportion of progeny will be chinchilla?

A)0%
B)10%
C)25%
D)50%
E)100%

Question 7

The diagram below shows a simplified version of the biochemical pathway responsible for fruit color in peppers.Assume that Enzyme 1 is encoded by gene A (a is a null allele),Enzyme 2 is encoded by gene B (b is a null allele),and Enzyme 3,which breaks down the chlorophyll present in the fruit,is encoded by gene C (c is a null allele).In the absence of Enzyme 3,the fruit takes a brown color in the presence of red pigment,but it remains green in the absence of red pigment.


Absence of chlorophyll

a) Consider two genotypically different pure lines that make colorless peppers.If these two plants are crossed,what phenotypes should be observed in the F₁?

A)colorless only
B)colorless and yellow only
C)red and yellow only
D)red only
E)yellow only

Question 8

Two new mutant lines of a flowering plant have been obtained; one breeds true for blue flower color and the other breeds true for red flower color (wild-type flower color is purple). Consider the following crosses.
1. blue $\times$ purple $\rightarrow F _ { 1 }$ all purple $\rightarrow F _ { 2 } 75 \%$ purple; $25 \%$ blue
2. red $\times$ purple $\rightarrow \mathrm { F } _ { 1 }$ all purple $\rightarrow \mathrm { F } _ { 2 } 75 \%$ purple; $25 \%$ red
3. red $\times$ blue $\rightarrow F _ { 1 }$ all purple

If the red pigment is a precursor of the purple pigment,the blue pigment is a precursor of the red pigment,and a colorless compound is the precursor of the blue pigment in a linear biosynthetic pathway controlling flower color,what phenotypic ratios do you expect in the F₂ of cross 3?

A)3 purple : 1 white (colorless)
B)9 purple : 3 blue : 3 red : 1 white (colorless)
C)9 purple : 4 blue : 3 red
D)9 purple : 7 white (colorless)
E)12 purple : 3 blue : 1 white (colorless)

Question 9

In the fruitfly Drosophila melanogaster,red and yellow eye pigments are synthesized through the pterin pathway.These,plus the brown pigment synthesized through the ommochrome pathway,produce the dark red Drosophila eye color.A part of the pterin pathway (simplified)is shown below.
Consider the genes encoding Enzyme 1 ("e1"),Enzyme 2 ("e2")and Enzyme 3 ("e3"),respectively.What are their predicted genetic interactions?

A)e1 is recessively epistatic to e2,and e2 is recessively epistatic to e3.
B)e1 is recessively epistatic to e3,and e3 is recessively epistatic to e2.
C)e3 is recessively epistatic to e1,and e2 is recessively epistatic to e1.
D)e1 is recessively epistatic to e2 and to e3.
E)e2 is recessively epistatic to e1 and to e3.

Question 10

Two new pure-breeding strains of mouse (strain 1 and strain 2)have been obtained.Crosses between strain 1 and wild type,as well as crosses between strain 2 and wild type and between strain 1 and strain 2 always produce 100% wild-type mice. What kind(s)of interactions can be deduced from these results?

A)complementation only
B)dominance only
C)epistasis only
D)complementation and dominance
E)complementation,epistasis,and dominance

Question 11

Crosses between two ducks with spread-out tail phenotype always produce ducklings with spread-out,normal,and pointy tails in a 2:1:1 ratio.In addition,normal-tailed ducks crossed to short-tailed ducks always produce only normal-tailed individuals,while crosses between pointy-tailed and short-tailed individuals always produce only pointy-tailed ducklings.If the tail shape phenotype is controlled by a single locus,what is the expected phenotypic ratio in the progeny of the cross spread-out tail × short tail?

A)1:0 of spread-out : short
B)1:1 of normal : pointy
C)1:1 of spread-out : short
D)1:1:1:1 of spread-out : normal : pointy : short
E)3:1 of spread-out : short

Question 12

When selfed,a particular plant always produces an F₁ with a phenotypic ratio of 2:1.If this plant is testcrossed,what is the expected phenotypic ratio in the progeny?

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

Question 13

The gene "C" codes for the membrane-associated protein C,responsible for signal transduction.A mutant allele of this gene,C^m,encodes a malfunctioning C protein,which has the same size as the wild type and associates with the plasma membrane like the wild type,but it has no function in signal.With respect to the expression of the C proteins,the wild-type allele is:

A)codominant to the C^m allele.
B)dominant to the C^m allele.
C)haploinsufficient.
D)incompletely dominant to the C^m allele.
E)recessive to the C^m allele.

Question 14

A 15:1 phenotypic ratio in a typical F₂ data set would be consistent with _____________________ affecting a particular phenotype.

A)incomplete dominance
B)codomininance
C)alleles of two genes
D)epistatic alleles
E)the environment

Question 15

In a flowering plant,gene "A" encodes an enzyme responsible for the presence of dots on the flowers' petals.A₁,A₂,and A₃ are the three known alleles of this gene;A₁ is the wild type,A₂ is a null allele,while A₃ has a mutation in the promoter region of the gene,which results in the synthesis of very little gene product. If the "A" gene is haploinsufficient,what is the predicted phenotypic ratio in the F₁ of a cross between a wild type and a A₂/A₃ heterozygous?

A)100% of the F₁ plants will have flowers with dots.
B)25% of the F₁ plants will have flowers with dots,and 75% will have flowers with no dots.
C)50% of the F₁ plants will have flowers with dots,and 50% will have flowers with no dots.
D)50% of the F₁ plants will have flowers with a few dots,25% will have flowers with normal amounts of dots,and 25% will have flowers with no dots.
E)100% of the F₁ plants will have flowers with no dots.

Question 16

In swine,when a pure-breeding red is crossed to a pure-breeding white,the F₁ are all red.However,the F₂ shows 9/16 red,1/16 white,and 6/16 as a new color-sandy.A particular red individual (Parent 1)is crossed to a particular sandy individual (Parent 2),and the progeny is comprised of four sandy,three red,and one white piglets.What are the most likely genotypes of the two parents?

A)A/A;B/B and A/a;B/b
B)A/A;B/b and A/a;B/b
C)A/A;b/b and A/a;B/b
D)A/a;B/b and a/a;B/B
E)A/a;b/b and A/a;B/b

Question 17

Pet rabbits can have a variety of coat colors.Below are the results of a series of crosses performed with black-,blue-,and brown-coated pure lines. $$\begin{array} { r l l } \text { Cross } & \text { Phenotypes of parents } & F _ 1{ \text { phenotypes } } \\1.&\text {Black } \times \text { blue } & \text { All black } \\2. & \text { Black } \times \text { brown } & \text { All black } \\3.&\text { Blue } \times \text { brown } & \text { All black }\end{array}$$
If the F₁ of cross number 3 is selfed,what is the expected proportion of black kits (baby rabbits)in the offspring?

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

Question 18

In chickens,the dominant allele Cr produces the creeper phenotype (having extremely short legs).However,the creeper allele is lethal in the homozygous condition.If two creepers are mated,what proportion of the living progeny will be creepers?

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

Question 19

Drosophila eyes are normally red.Several purple-eyed strains have been isolated as spontaneous mutants,and the purple phenotype has been shown to be inherited as a Mendelian autosomal recessive in each case.To investigate allelism between these different purple mutations,two purple-eyed pure strains were crossed.

If the purple mutations are in different genes (i.e.,they are not allelic),the phenotypic ratios in the F₁ are expected to be:

A)100% red.
B)75% red : 25% purple.
C)50% red : 50% purple.
D)25% red : 75% purple.
E)100% purple.

Question 20

The following non-complementing E.coli mutants were tested for growth on four known precursors of thymine,compounds A-D.The data provided in the table to reveal a simple linear biosynthetic pathway of the four precursors and the end product,thymine.In what order do the enzymes appear in this pathway (designate by their mutant number)? $$\begin{array} { | l | l | l | l | l | l | } \hline \text { Mutant } & \text { A } & \text { B } & \text { C } & \text { D } & \text { Thymine } \\\hline 9 & + & - & + & - & + \\\hline 10 & - & - & + & - & + \\\hline 14 & + & + & + & - & + \\\hline 21 & - & - & - & - & + \\\hline\end{array}$$

A)14,9,10,21
B)9,10,14,21
C)10,9,14,21
D)21,14,9,10
E)10,21,14,9

Question 21

A series of hamster crosses are performed to get an insight into the mode of inheritance of three coat colors: plain brown,plain beige,and patchy brown.Note that not all the parents were pure-breeding.
$\begin{array}{|l|l|l|}\hline \text { Cross } & \text { Parents phenotypes } & F_{1} \text { phenotypes } \\\hline 1 . & \text { Plain brown } \times \text { plain brown } & 14 \text { plain brown } \\\hline 2 . & \text { Plain beige } \times \text { plain beige } & 12 \text { plain beige } \\\hline 3 . & \text { Patchy brown } \times \text { patchy brown } & 6 \text { patchy brown, } 3 \text { plain brown } \\\hline 4 . & \text { Plain brown } \times \text { plain beige } & 13 \text { plain brown } \\\hline 5 . & \text { Patchy brown } \times \text { plain brown } & 6 \text { plain brown } 7 \text { patchy brown } \\\hline 6 . & \text { Plain beige } \times \text { patchy brown } &7 \text { plain brown, } 3 \text { patchy brown, } 3 \text { plain } \\&&\text { beige }\\\hline7. &\text { Plain beige} \times \text { plain beige}&\text { 9 plain beige}\\\hline8 . & \text { Plain brown } \times \text { plain brown } & 10 \text { plain brown, } 3 \text { plain beige }\\\hline\end{array}$

Propose a mode of inheritance for coat color in hamsters,using symbols of your own choosing to identify genes and alleles.Indicate relationships between alleles,and use the data above to support your explanation.

Question 22

The following example of gene regulation involves genes r⁺ and a⁺.Loss of either gene results in a similar phenotype.

a)In complementation testing,would these genes appear as one gene or two distinct genes? Explain.

b)What ratio might be generated by this example in a typical F₂ data set where an F₁ organism of phenotype r⁺/r ;a⁺/a had been selfed? Explain terms clearly.

Question 23

In Drosophila melanogaster,the dominant allele Cy results in curly wings.Interestingly,however,temperature also plays a significant role on the wing phenotype. $\begin{array}{llc}\text { Genotype } & \text { Temperature at } & \text { Proportion of individual } \\&\text { which raised }&\text { with curly wings }\\C y^{+} / C y^{+} \text {(wild type) } & 17^{\circ} \mathrm{C} & 0 \% \\C y^{+} / C y^{+} \text {(wild type) } & 26^{\circ} \mathrm{C} & 0 \% \\C y / C y^{+} \text {(mutant) } & 17^{\circ} \mathrm{C} & 15 \% \\C y / C y^{+} \text {(mutant) } & 26^{\circ} \mathrm{C} & 100 \%\end{array}$

Based on this information we can say that:

A)the expressivity and penetrance of the Cy allele are temperature-dependent.
B)the expressivity of the Cy allele is incomplete.
C)the expressivity of the Cy allele is temperature-dependent.
D)the penetrance of the Cy allele is incomplete.
E)the penetrance of the Cy allele is temperature-dependent.

Question 24

In humans,the ABO blood type is determined mainly by four alleles of one gene,defined by the following allelic series:
I^A = I^B > i.(I^A is codominant to I^B,and i/i results in blood type O).What matings can potentially produce children of any of the four blood types?

Question 25

A dihybrid plant is selfed,and the offspring shows a 13:3 phenotypic ratio for flower color.If the same dihybrid plant was testcrossed instead of being selfed,what would be the expected phenotypic ratio in the offspring?

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

Question 26

An A/a;B/b dihybrid is testcrossed,and about ¾ of the progeny phenotypically resembles the dihybrid parent,while ¼ resembles the tester parent.If the dihybrid parent was selfed,what would be the expected phenotypic ratio in the progeny?

A)9:3:4
B)9:7
C)12:3:1
D)13:3
E)15:1

Question 27

Two mutant,colorless strains of the (fictitious)haploid fungus Cyanomyces are crossed.The progeny consists of 50% wild-type (blue)and 50% mutant (colorless)spores.
a)How can this result be explained?
b)Based on your explanation in part a),what is the predicted result of a cross between a blue and a colorless strain?

Question 28

In sweet peas,the allele C is needed for color expression (c results in white).The precise color expressed is determined by the alleles R (red)and r (blue).A cross between certain red and blue plants resulted in progeny as follows: 3/8 red,3/8 blue,1/4 white.What were the genotypes of the plants crossed?

A)\ C/c;R/r $\times$ C/C;R/R
B)C/c;R/r $\times$ C/c;R/r
C)C/c;R/r $\times$ C/c;r/r
D)C/c;R/r $\times$ c/c;R/r
E)C/c;r/r $\times$ C/C;R/r

Question 29

In loppins (fictitious diploid invertebrates),ear shape is controlled by two genes with two alleles each;upright ears (F)is dominant to floppy ears (f),and double-pointed ears (P)is dominant to single-pointed ears (p).Moreover,due to genetic interactions,floppy ears are always single-pointed.A loppin with floppy ears is crossed to a loppin with upright single-pointed ears,and the phenotypic ratios in the offspring are 2 floppy : 1 double-pointed upright : 1 single-pointed upright.What are the genotypes of the parents?

A)p/p;f/f and p/p;F/f
B)P/p;f/f and p/p;F/F
C)P/p;f/f and p/p;F/f
D)P/P;f/f and p/p;F/F
E)P/p;F/f and p/p;F/f

Question 30

In the nematode C.elegans,homozygosity for the "e" mutant allele causes an extreme "uncoordinated" phenotype,where the worm completely loses its ability to move.Examination of 100 individuals with genotype e/e reveals that 58 of them can't move at all,45 show a very reduced ability to move,and the remaining 17 seem to have a completely wild-type phenotype with respect to movement ability.These observations suggest that e has:

A)high environmental components.
B)incomplete expressivity.
C)incomplete penetrance and variable expressivity.
D)low expressivity and variable penetrance.
E)low penetrance.

Question 31

You are studying loppins (fictitious but useful invertebrates)and are interested in the inheritance of the colorful dots on their abdomen.You notice that some loppins have no dots,some have green dots,some have orange dots,and some have a mixture of orange and green dots.

a)The first thing you notice is that it's relatively easy to obtain lines that breed true for the absence of dots,for the presence of orange dots only,or for the presence of green dots only,but it seems impossible to get pure-breeding loppins that have both green and orange dots.Every time that you cross two green-and-orange-dotted individuals,you obtain an F₁ comprised of about 50% green-and-orange-dotted,25% orange-dotted,and 25% green-dotted individuals.
What do you conclude? Explain your reasoning and use appropriate symbols to indicate the genotypes of the various individuals.

b)How could you determine genetically whether or not the "no dots" phenotype is allelic to "green dots," "orange dots," and "orange-and-green dots"? Outline the crosses that you would set up as well as the expected results if "no dots" was allelic versus if it was not allelic to the other phenotypes.

Question 32

Four pure lines of Guinea pigs (black,brown,gray,and tan)are used in a series of crosses.The results are as follows:


What is the expected phenotypic ratio in the F₁ of cross 6?

A)50% black females,50% black males
B)50% black females,50% gray males
C)50% black females,50% tan males
D)50% brown females,50% black males
E)50% tan females,50% tan males

Question 33

In a certain breed of dog,the alleles B and b determine black and brown coats,respectively.However,the allele Q of an unlinked gene is epistatic to the B and b color alleles,resulting in a gray coat (q has no effect on color).If animals of genotype B/b;Q/q are intercrossed,what phenotypic ratio is expected in the progeny?

A)1 black,2 gray,1 brown
B)3 black,12,gray,1 brown
C)4 black,9 gray,3 brown
D)9 black,1 gray,6 brown
E)9 black,4 gray,3 brown

Question 34

On an illegal wolf ranch in Wyoming,cowboys breed gray wolves and sell them illegally.A mutation was identified,generating a beautiful gray "speckled" coat color.The speckled wolves were particularly popular with buyers.The breeders struggled to keep up with demand.They noticed that when two speckled wolves were bred,their pups always contained some normal gray and some speckled gray pups.In one typical season of interbreeding the speckled wolves,they cumulatively generated 82 speckled and 38 gray pups.State a clear genetic explanation for the pattern illustrated.

Question 35

Domestic rats can have black,silver,or light-gray patches on their necks.A pure-breeding silver female was crossed to a pure-breeding black male,and the F₁ was comprised of black females and light-gray males.When F₁ brothers and sisters were mated,the resulting F₂ consisted of about ¼ black females,¼ black males,¼ silver females,and ¼ light-gray males.
Propose a model for the mode of inheritance of patch color in domestic rats.

Question 36

Below is a simplified version of the biochemical pathway responsible for fruit color in peppers.Suppose that gene A encodes enzyme 1,gene B encodes enzyme 2,gene C encodes enzyme 3,and that each gene only has two alleles: completely functioning (capital letters)and null (lower case letters).Note that red plus chlorophyll is brown,but yellow plus chlorophyll is green.

a)A breeder crossed two pure lines of peppers and then selfed the resulting F₁.The F₂ was comprised of 351 plants with red peppers,115 with yellow peppers and 154 with colorless (white)peppers.What must have been the genotypes and phenotypes of the two original pure lines?

b)A pure-breeding plant with green fruits is crossed to a pure-breeding plant that makes yellow fruits.All the F₁ plants make yellow fruits.The F₁ is selfed,and in F₂ we have 250 plants with yellow peppers,84 with colorless peppers,and 112 with green peppers.What must have been the genotypes and phenotypes of the original pure lines?

Question 37

In a flowering plant, the a/a ; B/B genotype results in yellow flowers, and the A/A ; b/b genotype gives red flowers. Wild-type flowers are orange and are observed in plants with genotype A/A ; B/B. Two possibilities have been proposed for the biosynthetic pathways of flower color:

1. yellow pigment $\rightarrow$ red pigment $\rightarrow$ orange pigment
2. red pigment $\rightarrow$ yellow pigment $\rightarrow$ orange pigment

Propose a genetic experiment that can determine which of the two possibilities is most likely correct, and explain how you would interpret your results.

Question 38

Suppose that pigmentation in rabbits is controlled by two genes (E and H).Each gene exhibits complete dominance,and the relationships between genotypes and phenotypes are listed below:
$$\begin{array} { l l } \text { Genotype } & \text { Phenotype } \\E /- ; H /- & \text { albino } \\e / e ; H / - & \text { brown } \\E / - ; h / h & \text { albino } \\e / e ; h / h & \text { albino }\end{array}$$
a)Two brown parents produce an albino baby rabbit.What are the genotypes of each of the parents and that of the kit (baby rabbit)?
b)What phenotypic ratio would be expected among the progeny of an intercross between dihybrid rabbits?
c)In a litter of five baby rabbits from the above cross,what is the probability that all five of the baby rabbits will be albino?

Question 39

In certain breeds of rabbits,the t/t genotype results in a specific malformation of the teeth.However,in any given rabbit population,only about 75% of the individuals with a t/t genotype actually have the teeth malformation.What is the penetrance of the t mutant allele?

A)75%
B)66.6%
C)50%
D)37.5%
E)25%

Question 40

In Drosophila,the recessive alleles for brown and scarlet eyes (of two independent genes)interact so that bw/bw;st/st is white.If a pure-breeding brown is crossed to a pure-breeding scarlet,what proportion of the F₂ will be white?

A)1/16
B)1/4
C)7/16
D)3/4
E)13/16

Question 41

Certain recessive genes cause profound deafness,and individuals homozygous for such genes are occasionally found in high frequencies among extended families in small,isolated communities.A deaf man and a deaf woman from two different communities,each having deaf parents,had three children,all of whom had normal hearing.
a)What are the parental genotypes?
b)What conclusions can be made about the allelic and gene interactions?

Question 42

Neurospora is a haploid,filamentous fungus normally having fluffy,orange masses of asexual spores called conidia.Two mutant strains,one having albino (white)conidia,and the other lacking conidia entirely (aconidial),were mated.Their progeny were as follows: 82 normal,86 albino,and 166 aconidial.
a)What are the parental genotypes?
b)What are the progeny genotypes and phenotypes?
c)What conclusions can be made about the gene interactions?

Question 43

The following four crosses all apply to diploid organisms.Assume that all the parents are true breeding.You are given the phenotypes of the parental generation and the phenotypic ratio of the F₂ generation.You must supply the following information.
1) genotypes of the parents
2) the phenotypic ratio expected for a testcross of the $F_{1}$
3) a diagram of the chromosomes of the $F_{1}$ in cross (c) at metaphase I Define your symbols.
a)
$\begin{array}{clll}\text { Pcross } & \text { Genotypes } & \text { Phenotypic } & \text { Testcross of } F_{1} \\& \text { of parents } & \text { Ratio in } F_{2} & \text { (phenotypic ratio, }\\\hline\text { Brown } \times \text { red }&\text {Brown }\underline{\quad\quad}&9 \text {red-brown}&\underline{\quad\quad}\\&&3\text {red}&\underline{\quad\quad} \\&\text {Red}\underline{\quad\quad}&\text {3 brown}&\underline{\quad\quad}\\&&\text {1 white}&\underline{\quad\quad}\end{array}$ b) $\begin{array}{clll}\text { Pcross } & \text { Genotypes } & \text { Phenotypic } & \text { Testcross of } F_{1} \\& \text { of parents } & \text { Ratio in } F_{2} & \text { (phenotypic ratio, }\\\hline\text { Red } \times \text {tall}&\text { Red }\underline{\quad\quad}&1 \text {red,tall}&\underline{\quad\quad}\\&&2\text {red, intermediate}&\underline{\quad\quad} \\&&2 \text { pink, tall }\\&\text {Tall}\underline{\quad\quad}&4\text { pink intermediate}&\underline{\quad\quad}\\&&2 \text {pink, short}&\underline{\quad\quad}\\&&1 \text {white, tall}\\&&2 \text {white, intermediate}\\&&1 \text {white, short}\end{array}$ c) $\begin{array}{llll}\text { Pcross } &\text { Genotypes }&\text { Phenotypic } & \text { Testcross of } F_{1}\\&\text { of parents }& \text { Ratio in } F_{2} & \text { (phenotypic ratio) } \\\hline\text { albino } 1 \times \text { albino } 2&\text { albino 1 }\underline{\quad\quad}&\text { 9 wild type }&\underline{\quad\quad}\\&&\text { 7 albino}&\underline{\quad\quad}\\& \text { albino } 2\underline{\quad\quad}\end{array}$ Diagram the chromosomes at metaphase I.Give all possible arrangements of the bivalents.Assume there is no crossing over between genes and centromeres.

Question 44

Loppins can be purple or white,and this phenotype is inherited as a simple dominant/recessive trait with complete penetrance.In females,purple is dominant over white,while in males the opposite is true.If you cross a white female to a purple male,and then you "self" the F₁ (i.e.,you cross brothers and sisters)what phenotypic ratios would you expect in the F₂? Assume that you always get a 1:1 ratio of males : females.

Question 45

In Drosophila,two genes affecting body color are known.A mutant allele at one locus prevents the formation of granules on which pigment is laid down.An absence of these granules causes an albino.Another gene causes the color (the pigment involved)to be blood-red.True-breeding albino males were crossed to true-breeding blood-red females.All males and females in the resulting F₁ generation were wild type in appearance.Two F₁ flies were intercrossed,producing a large F₂ generation,with the following phenotypes.

$\begin{array}{lll}\text { Phenotypes } & \text { Observed numbers } & \text { Expected ratic } \\\text { Wild-type female } & 39 & \underline{\quad\quad}\\\text { Blood female } & 8 &\underline{\quad\quad} \\\text { Wild-type male } & 13 & \underline{\quad\quad} \\\text { Albino male } & 17 & \underline{\quad\quad}\\\text { Blood male } & \underline{3}& \underline{\quad\quad}\\\text { Total } &{80} &16\end{array}$
a)What are the genotypes of the parents and the F₁?
b)Given the F₁ genotypes in part a),fill in the expected phenotypic ratio for the F₂ in the spaces above.
c)Use the chi-square test to determine how well the observed ratio fits the expected ratio.

Question 46

In wheat,a cross between red-kernel and white-kernel strains yielded F₁ offspring with red kernels.When the F₁ were intercrossed,the F₂ plants had a ratio of 15 red-kernel : 1 white-kernel.A testcross of the red-kernel plants yielded 3 red-kernel : 1 white-kernel.
a)What are the parental genotypes?
b)What are the F₂ genotypes and phenotypes?
c)What conclusions can be made about the allelic and gene interactions?

Question 47

Snapdragons with red,normally shaped flowers are mated with plants with white,abnormally shaped flowers.In the F₁,all the flowers are pink and have normal shape.The F₁ intercross yields the following F₂:
$$\begin{array} { l l } 3 / 16 & \text { red, nominal } \\6 / 16 & \text { pirk, normal } \\3 / 16 & \text { white, normal } \\2 / 16 & \text { pirk, abnormal } \\1 / 16 & \text { red, abnormal } \\1 / 16 & \text { white, abnormal }\end{array}$$
a)What are the parental genotypes?
b)What are the F₂ genotypes and phenotypes?
c)What conclusions can be made about the allelic and gene interactions?