The Dihybrid Cross

1. The Dihybrid Cross Two Pairs of Genes

2. Introduction • Method Used: • Punnett Square • Principle: • Complete Dominance • Data: Black fur is dominant to white fur. Curly fur is dominant to straight fur. Gene pairs: ( B-b ) ( C-c ) “B” stands for black “C” stands for curly “b” stands for white ‘c’ stands for straight

3. 4. List all the possible genotypes using B, b, C, c [from most to least dominant ] WE ARE GOING TO USE THE FOIL METHOD!!!!!! First…Outside…Inside…Last BC Bc bC bc Eggs BC Bc bC bc Sperm Gametes possible (”N”): BBCC BBCc BbCC BbCc BBcc Bbcc bbCC bbCc bbcc DESCRIBE EACH OF THESE INDIVIDUAL’S PHENOTYPE

4. A. Complete a Parent cross 1.) P cross 2.) 3.) BBCC x bbcc 4.) black,curly white, straight bc bc bc bc BC BC BC BC • Genotypes • BbCc : ------- • 16 : 0 BbCc BbCc BbCc BbCc BbCc BbCc BbCc BbCc • Phenotypes • Black,Curly:------- • 16 : 0 BbCc BbCc BbCc BbCc BbCc BbCc BbCc BbCc

5. F1 Cross • [cross between two individuals who are hybrid for two genes/traits] • (heterozygous black, heterozygous curly X heterozygous black, heterozygous curly) • [ BbCc ] x [ BbCc ]

6. BC Bc bC bc BC Bc bC bc 1.) F1 cross 2.) 3.) BbCc x BbCc 4.) Black, Curly Black, Curly BbCc BBCC BBCc BbCC BBCc BBcc BbCc Bbcc bbCC BbCC BbCc bbCc BbCc Bbcc bbCc bbcc

7. Calculate the genotype and phenotype ratios by counting: Genotype Ratio 1. BBCC 2. BBCc 3. BbCC 4. BbCc 5. BBcc 6. Bbcc 7. bbCC 8. bbCc 9. bbcc Phenotype Ratio 1. 2. 3. 4. 1 2 2 4 1 2 1 2 1 9 3 3 1 Black & Curly Black & Straight White & Curly White & Straight 9 : 3 : 3 : 1 1 : 2 : 2 : 4 : 1 : 2 : 1 : 2 : 1

8. We Aint Done Yet