dihybrid crosses: setting up punnett square
Post on 02-Jan-2016
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Dihybrid Crosses: Setting Up Punnett Square
• A cross involving two pairs of contrasting traits
• Round & Tall x wrinkled & Short (RrTt x rrtt)
• Use ‘FOIL’ method to find all combinations of alleles in the gametes
(First, Outer, Inner & Last)
• Ex. Heterozygous round & tall = RrTtGametes: RT, Rt, rT, rt
Rr Tt
First
Outer
Inner
Last
RTFirst
RtOuter
rTInner
rtLast
Legend
Round peas = RR, Rr
Wrinkled peas = rr
Yellow peas = YY, Yy
Green peas = yy
RrYy x RrYy
rryyrrYyRryyRrYy ry
Last
rrYyrrYYRrYyRrYY rY
Inner
RryyRrYyRRyyRRYy Ry
Outer
RrYyRrYYRRYyRRYY RY
First
ry
Last
rY
Inner
Ry
Outer
RY
First
Phenotype for a cross involving two parents that are heterozygous for both traits?
–9/16 Round,Yellow peas
–3/16 Round, Green peas
–3/16 Wrinkled, Yellow peas
–1/16 Wrinkled, Green peas
(56%)
(19%)
(19%)
(6%)
Ratio - 9:3:3:1
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