The boys all end up competing for Sheldon's sister, Missy's affection. Raj and Wolowitz even get into a physical fight.
A picture of Sheldon and his twin sister Missy (Courtney Henggeler) who definitely seems to have gotten the looks of the family.
Wolowitz tries to ask out Sheldon's sister Missy (Courtney Henggeler) when it becomes his turn and he gets shot down horribly. Poor Wolowitz.
Leonard and Wolowitz try desperately to hit on Sheldon's attractive twin sister Missy (Courtney Henggeler) without much success.

The Big Bang Theory Season 1 Episode 15 Quotes

Sheldon: You see, I'm a superior genetic mutation, an improvement on the existing mediocre stock.
Missy: And what do you mean, "mediocre stock?"
Sheldon: That would be you

Leonard: So, how do you two know each other?
Missy: He once spent nine months with my legs wrapped around his head.
Leonard: Excuse me?
Sheldon: She's my twin sister. She thinks she's funny, but frankly, I've never been able to see it.
Missy: That's because you have no measurable sense of humor, Shelly.
Sheldon: How exactly would one measure a sense of humor? A "humormometer?"