CROSSES INVOLVING MULTIPLE ALLELES
The best known example of multiple alleles involves the
gens for blood type in humans. This gene has three different
alleles and is located on Chromosome 9, two copies of which
exist in all human body cells. The alleles are as follow:
GENOTYPE PHENOTYPE (blood type)
1. IAIA or (AA) blood type A
2. IAi or (AO) blood type A
3. IBIB or (BB) blood type B
4. IBi or (BO) blood type B
5. IAIB or (AB) blood type AB
6. i i or (OO) blood type O
Sample Problem:
A woman with blood type A whose father was blood type O
married a man with type AB blood. What will be the possible
genotypes and phenotypes of their children?
Step 1: Determine genotypes of parents
Mom: ____ IAi _______
Dad: ____ IAIB ______
Step 2: Set up Punnett square
MOM
IA i
IAIA IAi
IAIB IBi
Problems:
1. A women HOMOZYGOUS for blood type B marries a man who is
HETERZYGOUS type A. What will be the possible genotypes and
phenotypes of their children?
IA
IB
Possible children genotypes:
IAIAIAi
IAIBIBi
Possible children phenotypes:
A, AO, AB, BO
