Unit 5 FRQ (Punnett Squares)

AP Bio Free Response Question for Punnett Squares

👋 Welcome to the AP Bio Unit 5 FRQ (Punnett Squares). These are longer questions, so grab some paper and a pencil, or open up a blank page on your computer. After you finish, you can see how you did with Unit 5 FRQ (Punnett Squares) Answers

⏱ The AP Biology exam has 6 free-response questions, and you will be given 90 minutes to complete the FRQ section. (This means you should give yourself ~15 minutes to go through each practice FRQ.)

• • 🤔 Need a quick refresher of the unit as a whole? Check out the Unit 5 Overview.
• • 😩 Getting stumped halfway through answering? Look through all of the available Unit 5 resources.

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Setup

The Eastern gray squirrel, Sciurus carolinensis, thrives in across the southeastern United States. Including their tails, they can be almost twenty-two inches long. They can live over a decade if they are not eaten by birds of prey, house pets, or even humans. A suburban neighborhood in the southern delta has an average population of squirrels, but many of the residents have begun to notice several of the squirrels do not have the characteristic long, bushy tails. Several of the neighborhood squirrels have skinny, hairless tails that resemble rat’s tails. A local biologist seeks to understand the mutation and begins trapping neighborhood squirrels to collect data. Over several months, the hundreds of squirrels are trapped, catalogued, and released. The data is summarized in Table 1. 

After careful research, the local biologist determines that the rat-tail is the result of a homozygous recessive genotype, commonly denoted as tt. The biologist hypothesizes that most squirrels have a heterozygous genotype of Tt for their tails. 

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Table 1

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Questions

(a) Assuming that the average squirrel is heterozygous, draw a Punnett square of two parent squirrels for tail type. Calculate the phenotypic and genotypic frequencies of the offspring. 

(b) Your Punnett square from Part A will define a specific number of expected rat-tailed squirrels. Using that as your expected value and the observed values from Table 1, calculate the Chi-square value for wild-type versus mutant phenotypes.

(c) In reference to your own calculations, explain if the local biologist’s hypothesis (that the average squirrel is heterozygous) is correct. 

(d) Squirrels are a species of rodent, which are characterized by teeth that are always growing for chewing and gnawing. They are closely related to rabbits, who dwell on the ground and are larger in size. Some rabbits, such as snowshoe hares (Lepus americanus), exhibit changes in fur color based on seasonal changes. Identify the phenomenon that results in these changes. 

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Answers & Rubric

💯 Ready to see how you did? Take a look at the Unit 5 FRQ (Punnett Squares) Answers.