In genetics, what does it mean for a line to be true-breeding for a trait?

• A. Offspring show the trait in every generation
• B. Offspring phenotype affected by environment
• C. Offspring require cross-pollination
• D. Offspring are heterozygous

Answer: (A)

True-breeding lines are homozygous for a trait, meaning all gametes carry the same allele for that trait. When such a line self-pollinates (or is crossed with an identical line), every offspring inherits the same two alleles and thus shows the same phenotype in every generation. The consistent outcome comes from fixed alleles in the line, not from environmental effects. Cross-pollination with a different genotype could introduce variation, and a true-breeding line cannot be heterozygous—that would prevent true-breeding and produce mixed offspring.