Final answer:
The probability of a child being a daughter with blood group O when both parents are heterozygous for blood group A is 1/8 or 12.5%.
Step-by-step explanation:
The question is asking for the probability of a child having a specific phenotype, in this case, a daughter with blood group O when both parents are heterozygous for blood group A (genotype IAi). We can calculate this using a Punnett square to determine the possible genotypes for the offspring. Each parent can pass on either the IA allele or the i allele. The possible combinations for the offspring would be IAIA, IAi, iIA, and ii. Because blood group O corresponds to the genotype ii, this is the only combination we are interested in. The possibility of ii occurring is 1/4, since there is a 50% chance of each parent passing on the i allele.
However, we also want the child to be a daughter. The probability of having a daughter is 1/2, because the sex of a child is determined by the chromosomal combination, with XX resulting in a female and XY resulting in a male, each having an equal chance of occurrence. To find the combined probability of having both a daughter and blood group O, we multiply the probability of each independent event.
The overall probability is (1/4) for blood type O times (1/2) for the child being a daughter, resulting in a probability of (1/4) * (1/2) = 1/8 or 12.5%.