A man with blood group A and his wife with blood group O had two children, and both were blood group A. The man decided that he had to be homozygous for the allele $I^A$, because he believed that if he were heterozygous then half of his children would have been blood group O. Why was this conclusion unsound?
- 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.