Section 6-5 Part 2 Dihybrid Crosses Write everything that is Yellow

Recall … Phenotype: The way an organism looks Black, white, tall short Genotype: The gene combination of an organism Homozygous Dominant, Heterozygous Homozygous recessive

Monohybrid Crosses: Dihybrid Crosses: A cross that involves Parents differ by just one trait (flower color) Dihybrid Crosses: A cross that involves 2 different traits (flower color AND plant height)

Naming Dihybrid Crosses Traits are written together in pairs All dominant traits are written first So, if a plant’s genotype is heterozygous tall (Tt) and heterozygous round (Rr), it would be written TtRr

Dihybrid Punnet Square In dihybrid crosses there are 4 possible allele combinations from each parent Each combination gets its own column or row

Setting up a Dihybrid Punnet Square Write all of this … Example Cross: TtRr x TTRR TR Tr tR tr TR TR TR TR

Filling in the Square TR Tr tR tr TR TTRR TTRr TtRR TtRr

Results: Phenotypes: All offspring are tall and round TTRR TTRr TtRR Genotypes: TTRR = 4 TTRr = 4 TtRR = 4 TtRr = 4 Phenotypes: All offspring are tall and round

Remember the The Law of Independent Assortment: Genes for different traits are inherited independently of each other When you have 2 or more different traits they are not “stuck” together

Example ll – long hair BB – Black Bb – Black bb - white LL – short hair Ll – short hair ll – long hair

BbLl Bb- Black Ll – short hair What are the genotypes of the offspring? What are the phenotypes? BbLl Bb- Black Ll – short hair

BbLL BbLl BBLL BBLl BBLl BBll BbLl Bbll bbLL bbLl BbLL BbLl Bbll bbLl bbll BbLl

BbLL BbLl BBLL BBLl Bbll BBll BbLl BBLl bbLl BbLL bbLL BbLl BbLl bbll Bbll bbLl