DIHYBRID GENETICS

Dihybrid Cross: Study of the inheritance of two gene pairs

Complications:Number of possible gametes increases

Number of Possible Gametes = 2n 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, TP or tp, tp, tp, tp

-gametes for each individual are the same because they are homozygous

F1 Genotypes: TtPp

F1 Gametes: formed from TtPp

Genes separate in meiosis (Law of Segregation)

Independent assortment allows for several combinations

Tt Pp Tt PpOR

F1 Genotypes: TtPp

Genes separate in meiosis – each gamete gets one of each gene

Independent assortment allows for several combinations

Tt Pp Tt PpOR

T P t p T p t P

Dihybrid Genotype results in 4 possible gametes.

Expands the Punnett to a 4x4 grid

FOIL the Gametes

TtPp

First =

Outer =

Inner =

Last =

FOIL the Gametes

TtPp

First = TP

Outer = Tp

Inner = tP

Last = tp

Possible gametes for:

TTPp = TtPP =

ttPp =

Possible gametes for:

TTPp = TP,Tp,TP,Tp

TtPP =

ttPp =

Possible gametes for:

TTPp = TP,Tp,TP,Tp

TtPP = TP,tP,TP, tP

ttPp =

Possible gametes for:

TTPp = TP,Tp,TP,Tp

TtPP = TP,tP,TP, tP

ttPp = tP,tp, tP, tp

F1 Cross: TtPp x TtPp

TP

TP

Tp

tPTp

tP

tp

tp

TP

TP

Tp

tPTp

tP

tp

tp

TTPP TTPp

TTppTTPp

TtPP

TtPP

TtPp

TtPp

TtPp

TtPp

Ttpp

Ttpp

ttPP

ttpp

ttPp

ttPp

Dihybrid Cross Ratios

Genotypic Ratio:

Phenotypic Ratio:

Dihybrid Cross Ratios

Genotypic Ratio:

TTPP:TTPp:TtPP:TtPp:TTpp:Ttpp:ttPP:ttPp:ttpp

Phenotypic Ratio:

Dihybrid Cross Ratios

Genotypic Ratio: TTPP:TTPp:TtPP:TtPp:TTpp:Ttpp:ttPP:ttPp:ttpp

1:2:2:4:1:2:1:2:1

Phenotypic Ratio:

Dihybrid Cross Ratios

Genotypic Ratio: TTPP:TTPp:TtPP:TtPp:TTpp:Ttpp:ttPP:ttPp:ttpp

1:2:2:4:1:2:1:2:1

Phenotypic Ratio:

Tall Purple: Tall White: Short Purple: Short White

Dihybrid Cross Ratios

Genotypic Ratio: TTPP:TTPp:TtPP:TtPp:TTpp:Ttpp:ttPP:ttPp:ttpp

1:2:2:4:1:2:1:2:1

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?