Download - Inheritance of Two Traits: Dihybrid Crosses
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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