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Inheritance of Two Traits:

Dihybrid Crosses

Learning goal:

Predict the inheritance patterns and combinations of alleles in gametes of individuals heterozygous for two traits.

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Determine the inheritance of two traits

• Two traits in pea plants are seed shape and seed color. – R is the allele for the dominant, round

shape characteristic; – r is the allele for the recessive, wrinkled

shape characteristic. – Y is the allele for the dominant, yellow

color characteristic; – y is the allele for the recessive, green

color characteristic.

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Distribution of alleles in gametesAssortment of Rr alleles • The gametes from the RrYy parent will receive one of the two

alleles Rr. • Half will receive the dominant R allele, and half the recessive r

allele.

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Distribution of alleles in gametesAssortment of Yy alleles • The gametes from the RrYy parent will also receive

one of the two alleles Yy. • Half will receive the dominant Y allele, and half the

recessive y allele.

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FOIL to determine gametesA quick way to determine the possible gametes

(R r) (Y y)F.irst of each set i * * RYO.uter allele of each * * Ry I.nner allele of each * * rYL.ast allele of each * * ry These combinations of alleles will go in the rows

or columns of your dihybrid Punnett square

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4. Cut in half the other way  

5. Cut each of those in half

Now you’re ready to set up the cross RrYy x RrYy

Draw your Dihybrid Punnett Square

1. Draw a rectangular box

2. Cut the box in half

3. Cut each half in half

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(Dom/Dom)

Round/Yellow:

(Dom/Rec)

Round/green:

(Rec/Dom)

wrinkled/Yellow:

(Rec/Rec)

wrinkled/green:

Phenotypic ratio

Dihybrid CrossDihybrid CrossFF

RYRYOORyRy

IIrYrY

LLryry

RYRY

RyRy

rYrY

ryry

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Dihybrid CrossDihybrid Cross

RRY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

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Dihybrid CrossDihybrid Cross

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio