20. Person #1 is of unknown blood type
as shown below.
a. It is possible that they could be
OO, as that would give the two children below.
b. It is possible that he is BO, as that would still give both
children.
c. It is possible that he is AO, as that would also give both
children.
d. Person #1 cannot be a genotype of AA nor BB as an AA parent
couldn't produce a Type B child, and a BB parent couldn't produce an Type A
child.
The genotype of person #1 is then OO,
BO, or AO.
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Slichter