1. Madison has type A blood, and so does her sister Abi. Her sister Marley has type O blood. A. What are Madison's parents' blood types? B. What is the genotype of Madison's blood?

A) Madison’s parents’ blood types may be either A & 0, or A & A.

B) Depending on her parents’ genotypes, Madison’s genotype may be either AA or A0

Explanation:

Since the A allele is dominant with respect to the 0, a person with blood type A may have either one (A0 genotype) or two A alleles (AA genotype). In contrast, a person with blood type 0 may only have two 0 alleles (00 genotype).

Because one of the sisters has type 0 blood, we have to assume that both of her parents have at least one 0 allele. There are two situations which may give rise to the described scenario (see Punnett squares):

Alternative 1: One of the parents has A blood type (A0 genotype), and the other has 0 blood type (00 genotype). Madison’s genotype may only be A0.

| 0 | 0

——————————

A | A0 | A0

——————————

0 | 00 | 00

Alternative 2: Both parents have A blood type and A0 genotypes. Madison’s genotype may be either A0 (probability of 2/3) or AA (probability of 1/3).

| A | 0

——————————

A | AA | A0

——————————

0 | 0A | 00