When a pure-tall pea plant is crossed with a pure-dwarf pea plant, the percentage of tall pea plants in $F_1$ and $F_2$ generation pea plants will be respectively :

When a pure-tall pea plant ($TT$) is crossed with a pure-dwarf pea plant ($tt$), all the offspring in the $F_1$ generation have the heterozygous genotype $Tt$. Since tallness ($T$) is a dominant trait, $100\%$ of the $F_1$ plants are phenotypically tall.

When these $F_1$ tall plants ($Tt$) are self-pollinated, the $F_2$ generation is produced with the genotypic ratio of $1\text{ }TT : 2\text{ }Tt : 1\text{ }tt$. Phenotypically, both $TT$ and $Tt$ are tall plants, while only $tt$ is a short plant. This results in a phenotypic ratio of $3\text{ tall} : 1\text{ short}$ (or $75\%$ tall and $25\%$ short). Thus, the percentage of tall plants in the $F_1$ and $F_2$ generations is $100\%$ and $75\%$ respectively.

• Why (c) is correct: It accurately states the percentages of tall plants in $F_1$ ($100\%$) and $F_2$ ($75\%$) generations.
• Why (a) is incorrect: $25\%$ is the percentage of short plants in the $F_2$ generation, not tall plants.
• Why (b) is incorrect: $50\%$ is the percentage of heterozygous tall ($Tt$) plants in the $F_2$ generation, not the total percentage of tall plants.
• Why (d) is incorrect: $100\%$ tall plants are only observed in the $F_1$ generation, as the recessive dwarf trait reappears in the $F_2$ generation.