What key event does Vincent undergo to maintain his deception as Jerome?

The key event that Vincent undergoes to maintain his deception as Jerome is providing blood and urine samples to pass genetic testing. In the context of "GATTACA," individuals are often subjected to rigorous genetic testing to determine their genetic identity and suitability for certain roles in society. In order to conceal his true identity as a naturally conceived individual who is considered "invalid," Vincent adopts Jerome's identity, which includes using Jerome's genetic samples.

By submitting blood and urine samples from Jerome, Vincent is able to successfully pass the genetic screenings that would otherwise reveal his true identity. This act is crucial to his plan to achieve his aspirations and defy societal expectations based on genetic predispositions. The focus on genetic identity is central to the film's themes of determination and the struggle against predetermined societal roles.