GENETICS NOTES: DIHYBRID CROSS
Definition: 2 traits; different (hybrid or heterozygous) for each.
Ex. Trait 1 = seed shape: R= Round , r = wrinkled
Trait 2 = seed color: Y = Yellow, y = green
RrYy x RrYy
a) Each parent gives one allele for each trait to offspring. So, each
gamete should have one “R” and one “Y”.
b) “FOIL” to determine possible gametes.
c)
d)
e)
f)
First = RY
Outer = Ry
Inner = rY
Last = ry
Since both parents have same genotypes (RrYy) the possible alleles
for each will be the same.
Determine # of squares in Punnett Square (42 = 16)
Draw Punnett Square
Add gametes to outside of Punnett Square
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
g) Conduct cross; following down and across fill in possible offspring.
h) Determine the different phenotypes.
Round + Yellow
=9
Round + green
=3
wrinkled+ Yellow = 3
wrinkled + green = 1
i) How many different types of genotypes are possible for this cross? List
them.
9 different genotypes for this cross.