In creating a transgenic line, what is the purpose of mating founders from pronuclear injection to wild-type?

• A. To produce offspring that have the transgene
• B. To remove the transgene
• C. To produce chimeras
• D. To reduce litter size

Answer: (A)

Germline transmission is what this step is about. When a transgene is added by pronuclear injection, the founder animal is often mosaic, meaning some cells (including some germ cells) may carry the transgene while others do not. To establish a stable transgenic line, you need proof that the transgene can be passed through the germline to offspring. Mating the founder with a wild-type partner tests exactly that: if any of the progeny inherit the transgene, it shows the transgene is present in the germ cells and can be transmitted to future generations. Those progeny then become the basis for the transgenic line. If none of the offspring carry the transgene, the founder likely does not transmit it through the germline.

This isn’t about removing the transgene, nor about creating chimeras, nor about reducing litter size. It’s about confirming that the transgene can be inherited and using that to establish a line.