If tall stem is dominant and dwarf stem is recessive, what will the first generation be when a pure tall plant is crossed with a dwarf plant?

Correct answer: All heterozygous tall

Use T for the dominant tall allele and t for the recessive dwarf allele. A pure tall plant has genotype TT, while a dwarf plant must be tt. The cross TT × tt gives only Tt offspring because the first parent can provide only T and the second can provide only t. Every F1 plant is therefore heterozygous and phenotypically tall. A and C incorrectly predict dwarf offspring, while D confuses heterozygous Tt with homozygous TT.