Genetic variation is when there are many offspring with different genetics, therefore some offspring might be able to adapt due to its genetics
Since Mary has a Type A blood, she is either AA or AO while John is either BB or BO. Since both John's parents are Type AB, he can only have the either A or B as an allele and not O so he is BB. Since John can only give the B allele, all of his children must have the B allele in their blood types. So the adopted one is the child with type A blood.
I think a frameshift mutation that occurs very early in a protein sequence would have an effect on the structure of the protein such that the primary, secondary, and tertiary structures would be altered. A frameshift mutation occurs when a protein is drastically altered because of an insertion or a deletion. Insertions and deletions cause a change in the length of a gene, which causes a shift in the codon reading frame.