Final answer:
The symbol 'F' in test cross refers to 'Filial', with F₁ indicating the first generation of offspring. This concept is crucial in a test cross to determine the homozygosity or heterozygosity of an organism expressing a dominant trait.
Step-by-step explanation:
The symbol "F" in the results of a test cross stands for Filial. Specifically, F₁ refers to the first filial generation in a cross; the offspring of the parental generation. In the context of a test cross, which is used to determine if an organism expressing a dominant trait is a homozygote or a heterozygote, the F₁ generation is the result of crossing a dominant-expressing organism with one that is homozygous recessive for the same trait. If the dominant-expressing organism is a homozygote, all F₁ offspring will display the dominant trait, indicating that they are heterozygotes. If the dominant-expressing organism is a heterozygote, the F₁ offspring will show a 1:1 ratio of heterozygotes and recessive homozygotes.