I
A
i
I
A
I
B
I
B
i
I
B
I
B
I
A
I
B
I
B
i
This worksheet gives you practice in problems dealing with incomplete dominance. Below is a complete
example for you to follow.
Important information: Codominant traits are different from simple dominant traits because
heterozygous individuals can have multiple dominant alleles. This results in both traits being
expressed simultaneously. There is also a recessive trait that can be present.
EXAMPLE:
Blood type:
Type A: I
A
I
A
or heterozygous A: I
A
i
Type B: I
B
I
B
or heterozygous B: I
B
i
Type AB: I
A
I
B
Type O: ii
Note:
I
A
denotes that the allele is a dominant allele form "A". The "A" protein will be made on the red blood cells.
I
B
denotes that the allele is a dominant allele form "B". The "B" protein will be made on the red blood cells
I
A
I
B
denotes that the individual has both forms of dominant alleles "A" and "B". Both proteins made.
ii denotes that the individual has both recessive alleles. No proteins made on red blood cell.
Parent A: Heterozygous A
Parent B: Homozygous B
Calculate the probability of each phenotype being passed down to the offspring.
INFORMATION:
Notice how the punnett square is set up so that one
parent has the genotype across the top.
The other parent's genotype is down the side.
The table is filled in according to the corresponding
genotype.
TOTALS:
A: 0 out of 4…….0/4
B: 2 out of 4……..2/4
AB: 2 out of 4……2/4
O: 0 out of 4…….0/4
If the question asks for a ratio, you must do the following:
-Use the total for that phenotype.
-Write the ratio with a labeled number.
Ratio for above problem: 0: 2:2:0
Ratio for above problem: 0A: 2B : 2AB : 0 O
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