Punnett Squares

By Sandra Craig on Nov 04, 2015

This activity provides students with a hands-on exercise that relies on shapes rather than the ability to read letters.  Color-coordination of foam pieces helps students who have color vision track what pieces go together, as well as allowing the instructor the opportunity to quickly assess student work.
 

Objectives

  1. Students will construct and analyze Punnett squares for monohybrid genetic crosses of given scenarios.  
  2. Students will analyze the expected genotypes and phenotypes that result from each cross.

 

Preparation:

  • Separate geometric shapes by color and size.  7 of each color, size and shape/Punnett Square/student will be needed.  Store sorted shapes in zip-lock bags for now.  
  • For eye color: Select a large egg (mother), place two large pink circle shapes in the egg, and close the egg.  This is homozygous dominant. In another large egg place two small pink circle shapes and close the egg.  This is homozygous recessive.  Select one more large egg and place one small and one large pink circle shape into the egg, and close it.  This one is heterozygous.  Repeat the process using small egg (father) and blue circles.  
  • Hair color: Same process as above but use the yellow-purple color pair.
  • Height: Same process as above but use the orange-green color pair.
(Don’t worry about having a large number of unused pieces.  The next time you do this activity, rotate the color pairs: eyes: yellow-purple; hair: orange-green; and height: pink-blue.  Save other shapes for future tactile graphic projects, or share with another teacher. Also save the left-over plastic eggs for another activity such as the “Scientific Method”)
 

Prepare the worksheet:  

Print the worksheet on card stock or other heavy paper (braille paper) in order to support the foam pieces.  For braille reading students, emboss the sheets using a braille writer and tracing wheel.  
 

Prepare the muffin tins:  

Put the remaining (there should be 4 of each) sorted shapes in individual cups of the muffin tin.  Put the pink circles on one side of the muffin tin, and on the blue circles on the other.  Have the large circles to the left of the small circles.  When the students have completed the first Punnett Square for determining eye color, put the remaining circles back in their zip-lock bags and put the shapes for hair color in the muffin tins.  Repeat this process for when they have completed the second Punnett Square and are ready for the ‘height’ Punnett Square. 

 

Materials

  • 3 Large plastic Easter eggs 
  • 3 Small plastic Easter eggs
    • (Explain to students that the size of the female ovum is much larger than the size of male sperm.)
  • Containers from which to draw eggs: baskets, bowls, plastic bags
  • Assorted self-adhesive foam geometric shapes of various sizes and colors (purchased from craft store). 
  • Zip lock bags to store the sorted foam shapes
  • Muffin tins (one per student or team) (It might be helpful to label one side ‘Mother’ and the other side ‘Father’.)
  • Punnett Square worksheets in large print and braille
 

Procedure

  1. Have a brief discussion with the class about heredity – how we inherit one-half of our traits from our mother and one-half from our father.  
  2. Explain the purpose of the Punnett Square is to predict possible outcomes if the parents possess particular alleles.  Tell the students that a large foam piece represents a dominant allele and a small one represents a recessive allele.   Most students understand dominant and recessive, but if there seems to be doubt, ask students to explain the difference between the two.  
  3. Student selects a ‘mother’ egg from the basket for eye color and places the foam pieces in the appropriate spots in the Punnett Square.  
  4. Use the proper vocabulary when the occasion arises.  For example: Describe that the mother is heterozygous (or homozygous dominant or homozygous recessive) and explain why.  
  5. Pass the worksheet around so everyone has a chance to examine it.
  6. Repeat the process for the ‘father’, select an egg, place the foam pieces, discuss his traits, and pass the worksheet around for students to examine.
  7. Stop and discuss the difference between genotype and phenotype.  What color are the mother’s eyes?  Brown Because… she’s heterozygous or homozygous dominant.  Or maybe Blue because… she’s homozygous recessive.  Ask the same questions about the father.
  8. Have students select the appropriate shapes (based on mother’s and father’s alleles) from the muffin tin and place the shapes in the Punnett square for the first offspring.  Pass the worksheet around for students to examine. Remind them that if there is a dominant trait, it should be place first. Ask students to describe the genotype and phenotype of offspring 1.
  9. Repeat the process for the remaining 3 offspring.
  10. If it appears that students understand the concept of the Punnett Square after completing the ‘Eye’ Punnett Square, hand out the ‘Hair Color’ worksheet, set up the muffin tins for that project, and allow them to beginning selecting the plastic eggs for mother’s and father’s alleles. If it seems they are still unclear, repeat the process for the hair color Punnett Square.  
  11. Intervene as needed.
  12. Check completed work and suggest corrections.  
  13. Hand out Punnett Squares Questions assignment.
eye color punnett squareeye color punnett square eye color punnett squarepungent square questions

Variations

  • When preparing the worksheet, make sure the size of the foam shapes matches with the size of the squares.
  • Remind students if there is a dominant shape and a recessive shape, place the dominant one on the left side of the box.
  • While reading the assignment, make the connections between the size of the foam piece we used and the letter shown in the text (large foam piece is now represented by a capitalized letter; small foam piece by a lower case letter).
  • If students are having difficulty transitioning from the shapes to letters only, use a Dyno labler and put braille letters on the shapes.  
  • Have on hand prepared Punnett Squares with both parents heterozygous; another with one parent homozygous recessive and one heterozygous; and a square with one parent homozygous dominant and one heterozygous.

NGSS Standards:

MS-LS3-2: Heredity: Inheritance and Variation of Traits
Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.  
 
LS3.B: Variation of Traits
In sexually reproducing organisms, each parent contributes half of the genes acquired (at random) by the offspring. Individuals have two of each chromosome and hence two alleles of each gene, one acquired from each parent. These versions may be identical or may differ from each other.
 
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