Answer: Maria has genotype of AO and Her sister have genotype of AB.
Step-by-step explanation:
Blood types are types of blood that are classified based on presence or absence of antigen on the surface of the red blood cells. For example type A blood contain one type of antigen which is A, type AB contain two type of antigen which is A and B.
Blood types are determined by genes or alleles(genotype).
Combination of alleles is called genotype.
A person with type A blood has dorminant allele that is he or she received A antigen from the parent.
From the examples Maria has O blood type. O allele is receive i.e it's always hidden in A or B alleles. Since the grandparents has A type therefore Maria have AO alleles .
Her sister is blood type AB be cause she receive both A and B allele from the parent.