WAEC Biology 2019 Papers

Concept:This is a dihybrid test cross between $RrTt$ and $rrtt$, where the recessive parent produces only one type of gamete.Explanation:The first parent $RrTt$ forms four gametes in equal ratio: $RT$, $Rt$, $rT$, and $rt$.The second parent $rrtt$ forms only one type of gamete: $rt$.When these gametes combine, four offspring genotypes appear in equal proportion.$RrTt$ gives red colour and tallness — 25% of the offspring.$Rrtt$ gives red colour and shortness — 25%.$rrTt$ gives non-red colour and tallness — 25%.$rrtt$ gives non-red colour and shortness — 25%.Thus, the proportion of offspring that are both tall and have red fruits is exactly one-fourth of the total.Answer:B. 25% tall with red fruits