Oscillation - [s12e15] The Donation

: Raj and Anu’s canceled bachelor party is repurposed into a group outing on a "Vomit Comet" (a weightless flight) for Raj, Anu, Howard, and Bernadette.

: After Leonard declines, Sheldon expresses interest in donating his "superior" genetic material, but Amy immediately shuts him down. [S12E15] The Donation Oscillation

: Penny’s father, Wyatt, visits and expresses his disappointment over her decision not to have children, adding pressure to the situation. : Raj and Anu’s canceled bachelor party is

: Ultimately, Leonard decides not to go through with it. He realizes he would be heartbroken to have a child in the world that he couldn't personally father. The "Vomit Comet" : Ultimately, Leonard decides not to go through with it

In the episode (Season 12, Episode 15), the story focuses on two main plotlines: Leonard’s potential sperm donation and a weightless "couple's trip" on a parabolic flight. The Donation Dilemma

: Although Penny initially said she was fine with it, she begins to have second thoughts. To prevent the donation—which requires Leonard to abstain from sex—she attempts to seduce him.