A man with blood group A and his wife, who has blood group O, had two children; both children were blood group A. He decided that he must be homozygous for the allele $I^A$, because he believed that, if he were heterozygous, half of his children would have group O. Why is his conclusion invalid?
- ABlood group mutations are common.
- BGenetic ratios are unreliable for small numbers.
- CHis wife might have been heterozygous.
- DThe expected ratio for a heterozygous father and group O mother is 3 group A : 1 group O.