Reese Witherspoon and 21-year-old daughter Ava Phillippe are about as much proof as possible that genetics work. Ivy Park Beam tweeted a holiday photo of the mother-daughter pair, saying, "I know this is how genes work but wow." The pair, who look strikingly similar, aren't the only celebrities who bear a strong resemblance to their kids, and people started posting similar pics on the thread of other celebs. Scroll down to see how strong these celeb genes really are.