DIHYBRID GENETICS Dihybrid Cross Study of the inheritance

DIHYBRID GENETICS

� Dihybrid Cross: Study of the inheritance of two gene pairs � Complications: Number of possible gametes increases Number of Possible Gametes = 2 n where “n” = number of gene pairs Monohybrid = 21 = 2 possible gametes Dihybrid = 22 = 4 possible gametes Trihybrid = 23 = 8 possible gametes Tetrahybrid = 24 = 16 possible gametes

Homozygous Tall plant with Purple Flowers X Homozygous short plant with white flowers � Key: T = Tall P = purple t = short p = white P Generation TTPP x ttpp Each gamete must get one of each gene Gametes: TP, TP, TP or tp, tp, tp � -gametes for each individual are the same because they are homozygous F 1 Genotypes: Tt. Pp

F 1 Gametes: formed from Tt. Pp Genes separate in meiosis (Law of Segregation) Independent assortment allows for several combinations Tt Pp OR Tt Pp

F 1 Genotypes: Tt. Pp Genes separate in meiosis – each gamete gets one of each gene Independent assortment allows for several combinations Tt TP Pp OR tp Tt Tp Dihybrid Genotype results in 4 possible gametes. Expands the Punnett to a 4 x 4 grid Pp t. P

FOIL the Gametes Tt. Pp First = Outer = Inner = Last =

FOIL the Gametes Tt. Pp First = Outer = Inner = Last = TP Tp t. P tp

Possible gametes for: TTPp = Tt. PP = tt. Pp =

Possible gametes for: TTPp = TP, Tp, TP, Tp Tt. PP = tt. Pp =

Possible gametes for: TTPp = TP, Tp, TP, Tp Tt. PP = TP, t. P, TP, t. P tt. Pp =

Possible gametes for: TTPp = TP, Tp, TP, Tp Tt. PP = TP, t. P, TP, t. P tt. Pp = t. P, tp, t. P, tp

� F 1 Cross: Tt. Pp x Tt. Pp

TP TP Tp t. P tp

TP TP Tp t. P tp Tp t. P TTPp Tt. PP Tt. Pp TTpp Tt. Pp Ttpp Tt. PP Tt. Pp tt. PP tt. Pp ttpp Tt. Pp Ttpp tp

Dihybrid Cross Ratios Genotypic Ratio: Phenotypic Ratio:

Dihybrid Cross Ratios Genotypic Ratio: TTPP: TTPp: Tt. PP: Tt. Pp: TTpp: Ttpp: tt. PP: tt. Pp: ttpp Phenotypic Ratio:

Dihybrid Cross Ratios Genotypic Ratio: TTPP: TTPp: Tt. PP: Tt. Pp: TTpp: Ttpp: tt. PP: tt. Pp: ttpp 1: 2: 2: 4: 1: 2: 1 Phenotypic Ratio:

Dihybrid Cross Ratios Genotypic Ratio: TTPP: TTPp: Tt. PP: Tt. Pp: TTpp: Ttpp: tt. PP: tt. Pp: ttpp 1: 2: 2: 4: 1: 2: 1 Phenotypic Ratio: Tall Purple: Tall White: Short Purple: Short White

Dihybrid Cross Ratios Genotypic Ratio: TTPP: TTPp: Tt. PP: Tt. Pp: TTpp: Ttpp: tt. PP: tt. Pp: ttpp 1: 2: 2: 4: 1: 2: 1 Phenotypic Ratio: Tall Purple: Tall White: Short Purple: Short White 9: 3: 3: 1 Phenotypic Ratio for ANY Dihybrid Cross where both parents are heterozygous for both traits.

A new species of spider was discovered in the boiler room of NDHS. These spiders either have large hairy bodies or small smooth bodies. They can also have red legs or brown legs. Extensive genetic research has shown that hairy bodies are dominant over smooth and brown legs are dominant over red. � If a smooth bodied male with brown legs (heterozygous) mates with a hairy bodied female (heterozygous) with red legs, what would the expected offspring look like? �

� If a purebred hairy bodied, red legged male spider is mated with a female that is heterozygous for both traits, how many offspring would be expected to have hairy bodies and red legs?