Here's why:

* True-breeding: This means the plants are homozygous for a particular trait. They will always produce offspring with the same trait when self-pollinated.

* F1 generation: This stands for "first filial generation." It refers to the first generation of offspring produced by crossing two true-breeding parents.

The F1 generation is always heterozygous for the trait in question. This means they have one copy of the dominant allele and one copy of the recessive allele.