Dihybrid Cross Notes
By Mr. W. Wright
• We Learned that a _______________
is crossing two organisms and looking at
__ trait.
• Mono =
• A ____________ is crossing two
organisms and looking at ___ traits.
• Di =
Example
H= allele for ______
1st Trait-
B= allele for _______
2nd Trait-
h= allele for _______
b= allele for _______
Consider the cross between to parents with the
following genotypes
HhBb
Bb
Parents: ________x
__________
We draw a punnett square.
H
B
H
b
h
B
b
B
b
HB B
Hb B
H BB
Hb B
H Bb
Hb b
H Bb
Hb b
hB B
hbB
h BB
h bB
hB b
hb b
h Bb
h bb
B
h
b
Phenotype Ratio:
9
3
3
1
Genotype Ratio:
Leave blank
As you can see, usually two parents that are heterozygous
for both traits are the hardest punnett squares
Example 2:
• A male with freckles and dimples mates with a female with
freckles but no dimples; what are the possible offspring.
F=allele for________
D=allele for _______
1st Trait
2nd Trait
f= allele for________
d=allele for_______
A Possible genotype cross may yield is …
Dd X FFdd
A punnett square may look like…
Parent phenotype:
F
d
F
d
F
d
F
d
D
d
D
d
FDd
Fd d
FD d
F dd
FDd
Fd d
FD d
F dd
FDd
Fd d
FDd
F dd
FD d
F dd
FD d
F d d
Phenotype Ratio:
8
8
0
Genotype Ratio:
Leave blank
0