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Question: butterflies have a zw mechanism of sex determination in this...

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Butterflies have a Z/W mechanism of sex determination. In this system, females are the heterogametic sex, so females are ZW and males are ZZ. Papilio glaucus, the Eastern Tiger Swallowtail, is found throughout the eastern United States. Papilio canadensis, the Canadian Tiger Swallowtail, is found throughout Southern Canada and the Northern United States. The two species are known to hybridize where their ranges overlap near the Great Lakes.

For butterflies living in seasonal environments, it is important to correctly time the diapause – a state of physiological dormancy that allows them to survive the winter. P. canadensis lives in colder climates and therefore has only one generation per year and an obligate diapause; all pupae of this species diapause from late fall until the next spring, when they resume development. In P. glaucus, most pupae diapause only in response to cold temperatures; as long as weather remains warm, they continue to develop. However, some P. glaucus pupae show obligate diapause similar to P. canadensis. The gene that controls diapause in Papilio is located on the Z chromosome, and obligate diapause is specified by the recessive allele ob.

A population of P. glaucus near Lake Michigan is at Hardy-Weinberg equilibrium. You have found that 9% of the male pupae show obligate diapause.

(1 point) What is the percentage of female pupae that show obligate diapause? (Show how you calculated this).

(1 point) What is the frequency of the ob allele in males and in females?

(1 point) What will be the frequency of obligate diapause pupae in the next generation in the absence of selection, in each sex?


(8 points) Winter came early and suddenly this year. Pupae that were in diapause because of the ob allele were safe, with a relative fitness of 1. Pupae that had not diapaused were much more susceptible to the cold and most of them died leaving them with a relative fitness of 0.2. All adults and other larvae died. What is the new frequency of the ob allele in the next generation? In males:

In females:

You now bring P. canadensis and P. glaucus back to the lab to carry out some controlled crosses. The P. canadensis population that you chose is fixed for the ob allele. The P. glaucus population that you chose is fixed for the alternative dominant allele at this locus that allows for environmental determination of diapause. From the following matings, what is the frequency of diapausing pupae that you would expect? (Show how you calculated this).

(2 points) Male canadensis x Female glaucus



(2 points) Male glaucus x Female canadensis



P.glaucus is highly palatable to predators. Females come in two forms: a yellow form that looks identical to males and has some level of crypsis and a dark form, which mimics the unpalatable butterfly Battus philenor. This trait is specific to females and the locus that determines the phenotype is biallelic and located on the W-chromosome.

(1 point) What form of mimicry is this?

(3 points) You are comparing two populations of P.glaucus found in different regions. What factors do you think might influence the relative fitness of the two morphs?

(1 point) What type of selection would you expect to act on the gene responsible for color morph determination? (check one)

Negative Frequency Dependent Selection

Positive Frequency Dependent Selection

Balancing Selection
Directional Selection

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