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Massachusetts Comprehensive Assessment System

2012, High School Biology

  Question 44: Open-Response  
In tomato plants, the allele for red fruit color (R) is dominant to the allele for yellow fruit color (r). The allele for round-shaped fruit (F) is dominant to the allele for pear-shaped fruit (f).Two tomato plants, heterozygous for fruit color and fruit shape, are crossed. The Punnett square for this dihybrid cross is shown below.
Punnett square with four columns and four rows. Column heading one is uppercase R, uppercase F. Column heading two is uppercase R, lowercase f. Column heading three is lowercase r, uppercase F. Column heading four is lowercase r, lowercase f. Row heading one is uppercase R, uppercase F. Row heading two is uppercase R, lowercase f. Row heading three is lowercase r, uppercase F. Row heading four is lowercase r, lowercase f. 
Row one, column one: uppercase R, uppercase R, uppercase F, uppercase F.
Row one, column two: uppercase R, uppercase R, uppercase F, lowercase f.
Row one, column three: uppercase R, lowercase r, uppercase F, uppercase F.
Row one, column four: uppercase R, lowercase r, uppercase F, lowercase f.
Row two, column one: uppercase R, uppercase R, uppercase F, lowercase f.
Row two, column two: uppercase R, uppercase R, lowercase f, lowercase f.
Row two, column three: uppercase R, lowercase r, uppercase F, lowercase f.
Row two, column four: uppercase R, lowercase r, lowercase f, lowercase f.
Row three, column one: uppercase R, lowercase r, uppercase F, uppercase F.
Row three, column two: uppercase R, lowercase r, uppercase F, lowercase f.
Row three, column three: lowercase r, lowercase r, uppercase F, uppercase F.
Row three, column four: lowercase r, lowercase r, uppercase F, lowercase f.
Row four, column one: uppercase R, lowercase r, uppercase F, lowercase f.
Row four, column two: uppercase R, lowercase r, lowercase f, lowercase f.
Row four, column three: lowercase r, lowercase r, uppercase F, lowercase f.
Row four, column four: lowercase r, lowercase r, lowercase f, lowercase f.
  1. For this cross, identify all the possible phenotypes of the offspring.
     
  2. Considering only fruit color, determine the ratio of offspring with red fruit to offspring with yellow fruit predicted by the Punnett square.
     
  3. Considering only fruit shape, determine the ratio of offspring with round-shaped fruit to offspring with pear-shaped fruit predicted by the Punnett square.
     
  4. Explain what is meant by independent assortment and describe one way in which your answers to parts (a), (b), and (c) support the conclusion that the genes for fruit color and fruit shape sort independently.

Scoring Guide and Sample Student Work
Select a score point in the table below to view the sample student response.

ScoreDescription
4 The response demonstrates a thorough understanding of how Mendel’s law of independent assortment can be observed through patterns of inheritance in dihybrid crosses. The response correctly identifies all the possible phenotypes and determines the ratios for fruit color and fruit shape. The response also clearly explains what is meant by independent assortment and describes one way in which the answers support independent assortment of the fruit color and fruit shape genes.
4
3 The response demonstrates a general understanding of how Mendel’s law of independent assortment can be observed through patterns of inheritance in dihybrid crosses.
2 The response demonstrates a limited understanding of how Mendel’s law of independent assortment can be observed through patterns of inheritance in dihybrid crosses.
1 The response demonstrates a minimal understanding of how Mendel’s law of independent assortment can be observed through patterns of inheritance in dihybrid 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.

High School Biology

Question 12: Evolution and Biodiversity
Question 23: Biochemistry and Cell Biology
Question 32: Anatomy and Physiology
Question 44: Genetics
Question 45: Ecology

Return to the MCAS 2012 Student Work Directory



Last Updated: August 19, 2016
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