NAME OF LESSON: Interactive Punnet Square

Subject Area: Genetics (biology)

Age or Grade: Middle school

Estimated Length: 1-2 class periods

Prerequisite knowledge/skills:

Students should understand the basic principles of independent assortment, dominant and recessive alleles, inheritance of traits, and the molecular genetics of genes (DNA). Student should also be familiar with plant reproduction (for example, our classroom had a large model of a plant so that students could identify stamen, pistel, etc.) and the Mendel pea plant experiments.

Description of New Content:

How to determine genotype, phenotype and percent offspring for a genetic cross between the alleles of two parents.

Goals:

Students should be able to successfully complete a punnet square regardless of the initial combination of pea plant alleles, and they should be able to answer the subsequent questions about genotype, phenotype and calculate percentages.

Materials Needed

· Punnet Square (blank page) – optional: laminate and add 2 velcro circles (soft side) to each blank spot for a classroom demo board

· Color-coded allele letters (light/dark shade combos for dominant/recessive alleles) – optional: laminate, cut apart each letter and add a Velcro sticker (rough side) to each letter for a classroom demo board.

*Laminated and color coded sheets with Velcro should be used for class demonstrations of the correct crosses, students should have their own blank punnet squares and allele letters which they can cut apart ahead of time and store in a ziplock bag. That way, students can try the crosses individually to start, and then a student can come to the front of the room and illustrate the cross on the large, Velcro board with color-coded alleles.

Procedure:

Students are given a parental genotype for the mother and father pea plants, which they should place on their blank punnet square (using the allele letters in their ziplock bag). The teacher decides which genotypes to use for the first few crosses, then students can suggest them. The teacher should also place the alleles on the master (laminated) punnet square at the front of the room. Students should be given a few minutes to solve the cross and answer the subsequent questions about percentages, ratios, phenotypes and genotypes for this particular cross. When they are finished, one student should volunteer to carry out the cross at the front of the room on the master punnet square.

Opener:

If we’re on a farm, and will be mating a female pea plant with purple flowers and a male pea plant with white flowers, how can I predict what color of flowers their offspring will have? (A: punnet square analysis!)

**Optional: If you can obtain actual flowering pea plants, it makes the lesson more life-like. There are also plant genetics kits available, so you can do your own life-like crosses in the classroom.

Development:

Start the activity using these alleles, then move onto other scenarios and alleles that students suggest.

Closure:

Not all crosses are this simple…we could do dihybrid crosses, or sometimes there is even incomplete dominance or codominance or other interesting inheritance patterns!

Evaluation:

Similar punnet squares can be given as a final evaluation for a grade.

Extensions:

Dihybrid crosses and more complicated crosses can be carried out for more advanced students. Advanced students also may want to create their own punnet square activity using another organism’s alleles.

References

Handouts:

Characteristic:

Flower color: P=purple, or p=white

P P P P P P P P

p p p p p p p p