JAMB Biology 2010 Paper

Concept:A monohybrid cross between two heterozygous parents gives the Mendelian genotypic ratio $1:2:1$.Explanation:Let the parents be $Aa \times Aa$.Each parent produces two types of gametes: $A$ and $a$.Combining the gametes gives these offspring genotypes: $AA$, $Aa$, $aA$, and $aa$.The ratio is therefore $1AA : 2Aa : 1aa$.Only the homozygous recessive genotype $aa$ expresses the recessive trait.Hence, the probability that an offspring will be recessive is $\frac{1}{4}$.Answer:C. $\frac{1}{4}$