Solving Genetic Problems Using Punnett Squares SBI3U: Genetic Processes

1. Solving Genetic Problems Using Punnett SquaresSBI3U: Genetic Processes Nushaye Henry & Jenny Kellar July 16, 2012

2. Why Study Genetics? • To predict the likelihood of inheriting particular traits.  • To help plant and animal breeders in developing varieties that have more desirable qualities.  • To help people explain patterns of inheritance in family lines.

3. Preparing to Learn About Punnet Squares • Students should have knowledge of Mendel’s experiments, including an understanding of: • a monohybrid cross between true-breeding parents • the P (parent) generation • first filial (F1) generation • second filial (F2) generation • the Law of Segregation • the Law of Independent assortment

4. Preparing to Learn About Punnett Squares • Students should also have an understanding of the following vocabulary: • Gene • Allele • Genotype • Phenotype • Dominant • Recessive • Homozygous • Heterozygous

5. The Punnett Square • Technique invented by an early 20th century English geneticist named Reginald Punnett. • One of the easiest ways to calculate the mathematical probability of inheriting a specific trait. • A graphical way of determining the potential genotypes of offspring, given the genotypes of their parents.  • It also shows us the odds of each of the offspring genotypes occurring.

6. Using the Punnett Square • Setting up and using a Punnett square is quite simple once you understand how it works.  • Begin by drawing a grid of perpendicular lines:

7. Place the genotype of one parent across the top and that of the other parent down the left side.  • Note that only one letter goes in each box for the parents.   • Example: if parent pea plant genotypes were YY and yy respectively, the setup would be:

8. Fill in the boxes by copying the row and column-head letters across or down into the empty squares.  • This gives us the predicted frequency of all of the potential genotypes among the offspring each time reproduction occurs.

9. Interpretation • In the previous example, 100% of the offspring will be heterozygous (Yy).  • Since the Y (yellow) allele is dominant over the y (green) allele for pea plants, 100% of the Yy offspring will have a yellow phenotype, as Mendel observed in his breeding experiments.

10. Curriculum Expectations By the end of this lesson sequence, students will be able to: • D2.1 Use appropriate terminology related to genetic processes, including, but not limited to: haploid, diploid, spindle, synapsis, gamete, zygote, heterozygous, homozygous, allele, plasmid, trisomy, non-disjunction, and somatic cell • D2.3 Use the Punnett square method to solve basic genetics problems involving monohybrid crosses, incomplete dominance, co-dominance, dihybrid crosses and sex- linked genes • D2.4 Investigate through, lab inquiry or computer simulation, monohybrid and dihybrid crosses and use Punnett square method and probability rules to analyze the qualitative and quantitative data and determine the parent genotype.

11. New Vocabulary Throughout this lesson sequence, students will learn and use the following: • Monohybrid cross • Dihybrid cross • Codominance • Incomplete Dominance • Sex Linkage • These definitions can be found in the accompanying Presentation Summary

12. Lesson Sequence Lesson1: Introduction to Punnett Squares • Review phenotype, genotype, dominant and recessive alleles • Use of “Get to Know Yourself” Power Point • Use of the Mouse Genetics (One Trait) Gizmo Lesson 2: Monohybrid Crosses continued/Introduction to Dihybrid • Review and Practice • What happens if we want to examine more than one trait? Lesson 3: Solving Dihybrid crosses with Punnett Squares • Use of Online Mix Those Genes game from The GEEE! In Genome website

13. Lesson Sequence (cont’d) Lesson 4: Complex Patterns of Inheritance • Co-dominance, Incomplete Dominance and Multiple Alleles • Genetic Traits in Harry Potter • Additional focus on blood types Lesson 5: Sex-Linked Traits • Monster Genetics Lab • Sex-linked Traits • Genetic Disorders

14. Teaching Strategy 1: Inquiry • Use of Power Point presentation and “Get to Know Yourself” worksheet • Students determine whether they display the dominant or recessive phenotype for a number of traits (hair colour, tongue rolling, ear lobes, freckles) and their possible genotypes

15. Teaching Strategy 2: Gizmo • Students complete the Gizmos Activity Mouse Genetics (One Trait) http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=449&ClassID=219230 • Other Gizmos applicable to this unit are Mouse Genetics (Two Traits) and Chicken Genetics (Codominance)

16. Teaching Strategy 3: Problem Solving Practice • Students complete a variety of genetic problems that require them to draw Punnett squares using good old fashioned….pencil and paper!

17. Teaching Strategy 4: Online Game • Students learn about dihybrid crosses using a simulation about eyecolour on The GEEE! in Genome website http://nature.ca/genome/04/041/041_e.cfm

18. Teaching Strategy 5: Monster Genetics Lab • Students flip a coin to determine the genotype of their monsters. They then use them to solve problems involving complex patterns of inheritance. http://www.nlm.nih.gov/exhibition/harrypottersworld/pdf/monstergeneticslab.pdf

19. Practical Applications • Breeds of dogs, varieties of vegetables, domestication of animals. A recent National Geographic article describes a long running experiment in which wild foxes were strategically bred until they became domesticated like dogs. http://ngm.nationalgeographic.com/2011/03/taming-wild-animals/ratliff-text/1paid • Ethical issues related to genomics, genetic testing or genetically modified organisms – these can be brought to life with films (ex: Gattaca or My Sister’s Keeper) or Case Studies. http://sciencecases.lib.buffalo.edu/cs/ • Examination of patterns of inheritance through families. • Solving questions of paternity or maternity.

20. Potential Student Difficulties • The use of uppercase and lowercase letters to represent dominant and recessive alleles rather than two different letters (for example T to represent tall, and t to represent short, rather than using T and S) Solutions: Proper modeling and continued practice • The use of superscript notation to solving problems that involve complex patterns of inheritance Solutions: Proper modeling by the teacher, continued practice, ensure that the resources students are given to help them use proper notation, as not all sources do. • Distinguishing between the concepts of codominance and incomplete dominance Solution: Use real-life examples

21. Accounting for Different Types of Learners • Use of a variety of strategies including Power Point presentations, diagrams, computer simulations, pencil and paper tasks, and real-life applications • ELL students will be paired with students who are proficient English speakers and speak their first language, a variety of visual resources will be available for their use • Flexible groupings will be used to ensure students work with a wide variety of peers • Additional support from teacher in a small group setting to reinforce concepts, when necessary

22. Differentiated Assessment • Quizzes, lab work, online activities, problem sets and in-class discussion will be used as formative assessment throughout the unit • Students will keep journals in which they will log their learning through their choice of method • A unit test will evaluate student understanding • Students may choose to present their understanding through a variety of products for the culminating task (poster, song, rap, video, brochure, game)

23. Resources • An extensive list of annotated resources can be found in the accompanying Presentation Summary