In 1980, y. published an extended pedigree of family in which
acis-ab allele was inherited . in one case they described a man
withtype o blood and a woman with type ab blood who had two
children, both with type o blood. calculate the probability of
thisparticular outcome (exactly two children with type o blood in
afamily of two children) given the phenotypes of the parents.

Zero (0)

Explanation:

According to the given information the genotype of the woman with blood type "AB" would by I^AI^B. The genotype of the man with blood type O would be "ii". Here, the alleles I^A and I^B are dominant over the allele "i".

A cross between parents with genotype I^AI^B and ii would give 50% of children with I^Ai genotype and 50% of children with I^Bi genotype. The children with "I^Ai genotype" would have blood type "A" and the children with I^Bi genotype would have blood type "B". This couple is never likely to have any child with blood type "O" since the mother does not carry allele "i".

Cross: I^AI^B x ii = 1/2 I^Ai : 1/2 I^Bi

the denominator has a very specific role.