DIHYBRID PUNNETT SQUARES https://www.youtube.com/watch?v=qIGXTJLrLf8

Dihybrid Cross: a cross that shows the possible offspring for two traits Trait one Trait Two Coat Texture: R: Rough r: Smooth Fur Color: B: Black b: White Step 1: FIND OUT THE GENOTYPES OF THE PARENTS In this example, we will cross a heterozygous individual with another heterozygous individual. Their genotypes will be: BbRr x BbRr

Dihybrid Cross BbRr x BbRr Step 2:FOIL EACH PARENT TO SHOW THE POSSIBLE GAMETE COMBINATIONS Remember, each gamete must have one B and one R. DAD MOM

F.O.I.L. PARENT 1 PARENT 2 BbRr BbRr Br br BR bR Br br BR bR

Practice What are the possible gametes for BBrr What are the possible gametes for HhTT?

BbRr x BbRr Dihybrid Cross DAD MOM Step 3:SET UP PUNNETT SQUARE: Arrange all possible gametes for dad on the top of your Punnett Square, and mom down the side

Dihybrid Crosses: a cross that shows the possible offspring for two traits BbRr x BbRr BR bR br Br Fur Color: B: Black b: White B B R R B B r R b B R R b B r R Coat Texture: R: Rough r: Smooth B B r r b B R r B B R r b B r r Step 4: Fill in the Punnett Square (find the possible genotypes of the offspring) B b R B b r R b b R R R b b r R B b R r B b r r b b R r b b r r

How many of the offspring would have a black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? BR bR br Br BBRR BbRR BbRr BBRr BBrr Bbrr bbRR bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

How many of the offspring would have black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? BR bR br Br BBRR BbRR BbRr BBRr BBrr Bbrr bbRR bbRr bbrr Phenotypic Ratio= 9:3:3:1 Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

Practice in your notes… In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r). Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

YyRr X yyrr YR yR yr Yr YyRr yyRr yyrr Yyrr

More Practice Work on the SpongeBob Dihybrid Cross worksheet. Turn it in at the end of class.