Question 1

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.

Accepted Answer

The answer of A series of hamster crosses are performed...

Question 2

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.

Accepted Answer

The answer of The following example of gene regulation involves...

Question 3

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.

Accepted Answer

The answer of In Drosophila melanogaster,the dominant allele Cy results...

Question 4

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?

Accepted Answer

The answer of In humans,the ABO blood type is determined...

Question 5

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

Accepted Answer

The answer of A dihybrid plant is selfed,and the offspring...

Question 6

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

Accepted Answer

The dihybrid testcross results suggest that the genes are linked, with the majority of progeny resembling the dihybrid parent. When the dihybrid is selfed, the expected phenotypic ratio for linked genes with complete dominance is 15:1.

Question 7

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?

Accepted Answer

The answer of Two mutant,colorless strains of the (fictitious)haploid fungus...

Question 8

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

Accepted Answer

The answer of In sweet peas,the allele C is needed...

Question 9

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

Accepted Answer

The phenotypic ratios in the offspring of 2 floppy : 1 double-pointed upright : 1 single-pointed upright suggest that the parents are heterozygous for both genes. Only choice C (P/p;f/f and p/p;F/f) fits this requirement. The first parent is heterozygous for the ear shape gene (F/f) and homozygous recessive for the ear point gene (p/p). The second parent is homozygous dominant for the ear point gene (F/F) and heterozygous for the ear shape gene (F/f). When these parents produce offspring, the possible combinations of alleles that result in each phenotype are:
- 2 floppy: f/p x f/p
- 1 double-pointed upright: F/P x f/p, F/p x P/f, f/P x P/f
- 1 single-pointed upright: F/p x f/p, f/p x F/f
These ratios match the ones observed in the offspring, confirming that choice C is the correct answer.

Question 10

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.

Accepted Answer

The fact that not all individuals with the e/e genotype exhibit the extreme uncoordinated phenotype suggests incomplete penetrance. The variable expressivity is evident in the fact that some individuals have a completely wild-type phenotype while others have a very reduced ability to move or can't move at all. The environmental component cannot be determined from the given information, and there is no evidence of low expressivity or low penetrance.

Question 11

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 F₁comprised 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.

Accepted Answer

The answer of You are studying loppins (fictitious but useful...

Question 12

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 F₁of 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

Accepted Answer

The answer of Four pure lines of Guinea pigs (black,brown,gray,and...

Question 13

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

Accepted Answer

The Q allele is epistatic and masks the effect of the B and b alleles, resulting in a gray coat. The expected phenotypic ratio when B/b;Q/q individuals are intercrossed is 3 black (B/-;q/q), 12 gray (Q/-), and 1 brown (b/b;q/q).

Question 14

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.

Accepted Answer

The answer of On an illegal wolf ranch in Wyoming,cowboys...

Question 15

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 F₁brothers 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.

Accepted Answer

The answer of Domestic rats can have black,silver,or light-gray patches...

Question 16

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?

Accepted Answer

The answer of Below is a simplified version of the...

Question 17

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.

Accepted Answer

The answer of In a flowering plant, the a/a ;...

Question 18

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?

Accepted Answer

The answer of Suppose that pigmentation in rabbits is controlled...

Question 19

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%

Accepted Answer

Penetrance is defined as the percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype. Since 75% of the rabbits with the t/t genotype show the teeth malformation, the penetrance of the t mutant allele is 75%.

Question 20

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

Accepted Answer

The cross between a pure-breeding brown (bw/bw;+/+) and a pure-breeding scarlet (st/st;+/+) will produce F1 offspring that are all heterozygous for both traits (bw/+;st/+). When these F1 individuals are crossed (F1 x F1), the proportion of offspring that are homozygous recessive for both traits (bw/bw;st/st) and thus white-eyed is 1/4 (for bw/bw) * 1/4 (for st/st) = 1/16.

Quiz 6: Gene Interaction

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?

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?

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?

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 F₁of cross 6?

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?

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?

Quiz 6: Gene Interaction

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

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?

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?

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?

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?

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?

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?

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 F₁of cross 6?

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?