WAEC Biology 2017 Papers

Concept:A cross between a heterozygous normal parent and an albino parent gives a $1:1$ ratio of normal to albino offspring.Explanation:The albino allele is recessive, so an albino child must have the genotype $aa$.For a child to be $aa$, both parents must contribute an $a$ allele.If one parent is heterozygous $Aa$ and the other parent is homozygous recessive $aa$, the cross is $Aa \times aa$.The $Aa$ parent produces gametes $A$ and $a$.The $aa$ parent produces only gametes $a$.The offspring genotypes are $Aa$ and $aa$ in equal proportion.Therefore, $50\%$ of the offspring are normal ($Aa$) and $50\%$ are albino ($aa$).Answer:B. $Aa, aa$