In generation nomenclature for transgenic lines, what does F1 denote?

• A. The founder's generation
• B. The first filial generation derived from the founder
• C. The second generation
• D. A backcross line

Answer: (B)

F1 denotes the first filial generation, the offspring produced when the founder (the parental line) is crossed with another line. It is the generation immediately after the founder, not the founder itself. The second generation would be F2, and a backcross line results from crossing an F1 back to one of the parental lines. Therefore, F1 is the first generation derived from the founder.