WAEC Biology 2022 Papers

Concept:Tall is dominant ($T$) and short is recessive ($t$).Explanation:Both original plants are tall, so neither parent can be $tt$.Since all F₁ plants are tall, every F₁ plant must have at least one $T$ allele.When the F₁ plants were selfed, short plants appeared in the F₂ generation.Short plants have genotype $tt$, so each F₁ parent must carry the recessive allele $t$.Therefore, some F₁ plants must be heterozygous, $Tt$.These $Tt$ F₁ plants can be produced only if the original parents are $TT$ and $Tt$.The cross $TT \times Tt$ gives all tall F₁ offspring: $TT$ or $Tt$.Selfing the $Tt$ F₁ plants gives both tall and short F₂ plants.Thus, the original genotypes must be $TT$ and $Tt$, not a combination involving $tt$.Answer:D. $TT$ and $Tt$