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Exam 6: Gene Interaction

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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.

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a)Most likely,green (c^G)and o...

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Question 2

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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

F) A) and E)
G) C) and D)

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Question 3

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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.

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?

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?

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?

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?

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 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.

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?

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.

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?

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.

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?

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?

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?

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:

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?

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?

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: