1. How to a Work Punnett Square A Step by Step Process

2. Sample Problem # 1 Predict the genotypic and phenotypic outcome (offspring) of a cross between two heterozygous tall (Tt) pea plants. 1 st : Decide which letters you will use to represent the alleles Allele Key: Tall = Short = T t Special Note: you don’t always have to use the letter T!

3. 2 nd : Write the phenotype of each parent Hetero tallx Hetero tall 3 rd : Write the genotype of each parent under the phenotype Tt x Tt

4. 4 th : List the alleles and their probabilities that each parent can contribute ½ T ½ T ½ t ½ t Hetero tallx Hetero tall Tt x Tt

5. ½ T 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ T ½ t

6. ½ T 6th: To solve the Punnett Square, multiply the separate probabilities and place the alleles in each box. ½ T ½ t ¼ TT

7. ½ T 6th: To solve the Punnett Square, multiply the separate probabilities and place the alleles in each box. ½ T ½ t ¼ Tt

8. ¼ TT ¼ Tt ½ T 6th: To solve the Punnett Square, multiply the separate probabilities and place the alleles in each box. ½ T ½ t ¼ Tt

9. ¼ TT ¼ Tt ½ T 6th: To solve the Punnett Square, multiply the separate probabilities and place the alleles in each box. ½ T ½ t ¼ tt

10. ¼ TT ¼ Tt ¼ tt ½ T 7 th : Write the genotypic ratio. Combine like terms when possible. ½ T ½ t 1 TT : 2 Tt: 1 tt

11. ¼ TT ¼ Tt ¼ tt ½ T 8 th : Write the phenotypic ratio. Combine like terms when possible. ½ T ½ t 3 tall : 1 short tall short

12. Sample Problem # 2 Predict the genotypic and phenotypic outcome (offspring) of a cross between a heterozygous round seed plant and a wrinkled seed plant. 1 st : Decide which letters you will use to represent the alleles Allele Key: Round = Wrinkled = R r

13. 2 nd : Write the phenotype of each parent Hetero roundx Pure Wrinkled 3 rd : Write the genotype of each parent under the phenotype Rr x rr Hetero roundx Pure Wrinkled

14. 4 th : List the alleles and their probabilities that each parent can contribute ½ R ½ r ½ r ½ r Hetero roundx Pure Wrinkled Rr x rr

15. ½ R 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ r

16. ½ R 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ r ¼ Rr

17. ½ R 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ r ¼ Rr

18. ½ R 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ r ¼ Rr ¼ rr

19. ½ R 5 th : Write the possible alleles and their probabilities of one parent across the top of the Punnett Square and the possible alleles and their probabilities along the side of the Punnett Square. ½ r ¼ Rr ¼ rr

20. ½ R ½ r ¼ Rr ¼ rr 7 th : Write the genotypic ratio. Combine like terms when possible. 2 Rr : 2 rr OR 1 Rr : 1 rr

21. ½ R ½ r ¼ Rr ¼ rr 7 th : Write the phnotypic ratio. Combine like terms when possible. 2 round : 2 wrinkled