If a tall pea plant is crossed with a dwarf pea plant and all plants in the first generation are tall what can be concluded?

Correct answer: Tallness is the dominant trait

In a Mendelian cross, a dominant allele expresses its trait in a heterozygous offspring, whereas a recessive allele can remain masked. If a tall plant is crossed with a dwarf plant and every F₁ offspring is tall, the observed phenotype indicates that tallness is dominant under the usual pure-parent assumption. Dwarfness is therefore recessive, not destroyed. Options C and D contradict the observed F₁ result.