Genesis is in the Old Testament, but many Christians will tell you they believe in Adam and Eve and the story of Noah's ark. Christians don't just go by the New Testament.
There are a bunch of silly laws in Leviticus, but many conservatives and fundamentalists believe that homosexuality is a sin, even though they will eat fat, touch an unclean animal, drink alcohol in religious places (What about the blood of Jesus?), etc. People believe what they want throughout the Bible, yet ignore large quantities of it.