WAEC Biology 2010 Papers

Concept:Albinism is a recessive trait. An albino child can be born only when the child inherits the recessive allele from both parents.Explanation:Let $A$ represent the normal skin colour allele.Let $a$ represent the recessive albino allele.Both parents have normal skin colour but are heterozygous for the gene.So, the genotype of each parent is $Aa$.The cross between the parents is written as:$Aa \times Aa$The possible gametes from each parent are $A$ and $a$.Combining these gametes gives the possible offspring genotypes:$AA$, $Aa$, $aA$, and $aa$.The genotypes $AA$, $Aa$, and $aA$ all show normal skin colour.Only the genotype $aa$ results in an albino child.Out of the 4 equally likely outcomes, only 1 outcome gives albinism.Therefore, the probability of having an albino child is:$\frac{1}{4}$.Answer:$\frac{1}{4}$, which is option B.