Massachusetts Comprehensive Assessment System

2018, High School Biology

Question 45: Open-Response

Reporting Category: Genetics
Standard: 3.6 - Use a Punnett Square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses.

Corn kernels can be high in starch (starchy) or high in sugar (sweet). The allele for starchy kernels (H) is dominant to the allele for sweet kernels (h).

Each kernel on an ear of corn represents an individual offspring. A particular ear of corn has 92 starchy kernels and 88 sweet kernels.

What are the most likely genotypes of the parent corn plants that produced this particular ear of corn?
Explain how you determined the genotypes of the parent corn plants in part (a). Draw a Punnett square for the cross to support your answer.
Identify the genotypes for two corn plants that, when crossed, will produce plants with 100% starchy kernels.

Scoring Guide and Sample Student Work

Select a score point in the table below to view the sample student response.

Score	Description
4	The response demonstrates a thorough understanding of how to use a Punnett square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses. The response correctly identifies the most likely genotypes of the parent corn plants, and clearly explains the answer with a correctly drawn Punnett square. The response also correctly identifies the parent genotypes that will produce plants with 100% starchy kernels.
4
3	The response demonstrates a general understanding of how to use a Punnett square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses.
2	The response demonstrates a limited understanding of how to use a Punnett square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses.
1	The response demonstrates a minimal understanding of how to use a Punnett square to determine the probabilities for genotype and phenotype combinations in monohybrid crosses.
0	The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured.

Note: There are 2 sample student responses for Score Point 4.

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Question 44: Ecology

Question 45: Genetics

Return to the MCAS 2018 Student Work Directory

Last Updated: March 11, 2024