WAEC Biology 2016 Papers

Concept:Each offspring inherits one allele from each parent. The parents' genotypes must be able to produce all the observed offspring genotypes: $\mathrm{AB}$, $\mathrm{BB}$, $\mathrm{BO}$, and $\mathrm{AO}$.Explanation:The offspring include $\mathrm{BB}$, so each parent must carry the $B$ allele.The offspring include $\mathrm{AO}$, so one parent must supply $A$ and the other must supply $O$.The offspring also include $\mathrm{AB}$ and $\mathrm{BO}$, which are formed when one parent contributes $A$ and the other contributes $B$, or one contributes $B$ and the other contributes $O$.Therefore, one parent must have genotype $\mathrm{AB}$ and the other must have genotype $\mathrm{BO}$.A cross between $\mathrm{AB}$ and $\mathrm{BO}$ produces $\mathrm{AB}$, $\mathrm{AO}$, $\mathrm{BB}$, and $\mathrm{BO}$ in the offspring.This matches all the listed offspring blood groups.Answer:$\mathrm{AB}$ and $\mathrm{BO}$.