Dopamine is a neurotransmitter or a chemical made in the brain that gives us feelings of reward and pleasure. The dopamine receptor D4 binds dopamine and transmits the signal into the cells.
The seven repeat version (7R) of the dopamine receptor D4 binds dopamine less efficiently than the common version 4R, therefore transmits reduced levels of signals in the brain. Individuals with the longer versions of DRD4, therefore require higher levels of dopamine to have the same effects. These longer versions are also associated with increased promiscuity and intriguingly sexual activity can influence dopamine levels.