2. PUNNET SQUARES

3. “The law of Independent Assortment” Alleles of different genes separate completely from one another during gamete formation XY X Y

4. white flower. Which means in Mendel’s flower experiments, he took a purebred purple flower and crossed with a purebred white flower. P = Purple color p = white color = = PPHomozygous dominant ppHomozygous recessive

5. The purple flower would separate into - PP PP The white flower would separate into - pp pp

6. A Punnett square - is used to predict the outcome of a genetic cross by considering all the possible combinations of alleles in the cross. We are just going to concentrate on 1 trait for now. So our cross would be PP x pp PurpleWhite

7. A FEW RULES ABOUT PUNNET SQUARES 1. Alleles are listed alphabetically. 2.Dominant traits always are written before recessive for that allele. Rr rR

8. So let’s go back to our cross PP x pp PurpleWhite Draw the punnet square on your notes.

9. When using a punnett square, you take the first set of alleles and put them on top. PP X pp P P Then take the 2 nd set of alleles and put them on the left side. p p

10. Now add each letter into the corresponding box. P P p p Pp

11. Purple (P) is dominant over white (p) So what is the phenotype of all the offspring? PP p p Pp All Purple

12. PP p p Purple (P) is dominant over white (p) So what is the genotype of all the offspring? Pp All Pp

13. When looking at Mendel’s flower experiment, he crossed the P1 purple with the P1 white flower and got 100% purple flowers. X P1P1 F1F1

14. When doing the punnett square, we predicted they would all be 100% purple. We were right! PP p p Pp

15. Then Mendel decided to cross a F1 purple flower with another F1 purple flower. So let’s try this with a punnett square. PP p p Pp

16. Pp X Pp P P p p PP Pp pp P – dominant P - recessive

17. P P p p PP Pp pp What is the Phenotype for this cross? 1 white 3 Purple to 1 white

18. What is the genotype for this cross in %? P P p p PP Pp pp 25 % = PP (homozygous dominant) 1 out of 4 50% = Pp (heterozygous) 2 out of 4 25 % = pp (homozygous recessive) 1 out of 4

19. Mendel got a 3 Purple : 1 white from his experiments X F1F1 3 Purple : 1 White

20. Using our punnett square, we proved Mendel was correct. P P p p PP Pp pp

21. Now let’s determine the sex of a baby! XY = maleXX = female X X X Y XX XY XX XY

22. What is the Phenotype of the baby? 50% male50% female What is the Genotype of the baby? 50% XY 50% XX

23. Question: If the first baby is a boy, what is the chance the second child will be a boy? X X X Y XX XY XX XY Answer: 50% - every time you have a baby, you start all over

24. Let’s practice a few Punnett squares to make sure you got it. Do the following crosses on your paper and give me the phenotype and genotype for the possible outcomes.

25. Tall plants (T) are dominant over short plants (t). Cross a purebred Tall with a hybrid Tall. TT x Tt T T T t TT Tt Phenotype 100% Tall Genotype 50% TT 50% Tt

26. Green Peas (G) are dominant over Yellow Peas (g) Cross a Hybrid Green Pea with a Hybrid Green Pea G g G g GG Gg gg Phenotype 25% - GG 50% - Gg 25% - gg Gg x Gg 3 Green: 1 yellow Genotype

27. Black hair (B) is dominant to blonde hair (b) Cross a homozygous recessive blonde with a heterozygous black haired person. bb x Bb b b B b Bb bb Bb bb 50% black haired 50% blonde 50% - Bb 50% - bb Phenotype Genotype

28. VOCABULARY ! Law of Independent Assortment Punnett Square

29. OK, let’s try a Spongebob Squarepants worksheet