O parents cannot conceive a B child as o is a recessive trait so therefore both these parents are pure breeding for their o group = both oo genotype.

Regarding the rhesus factor a negative child can only result from this combination if the o+ parent is a carrier for the neg. Allele (+ - ) and the child therefore receives two copies of the neg allele. But if the + parent is homozygous dominant for the pos. Then a neg child is impossible.

Regarding the rhesus factor a negative child can only result from this combination if the o+ parent is a carrier for the neg. Allele (+ - ) and the child therefore receives two copies of the neg allele. But if the + parent is homozygous dominant for the pos. Then a neg child is impossible.