The "wanderlust gene" is a genetic variant of the DRD4 gene. DRD4 encodes the dopamine receptor D4, and variation can occur in a repeat region of DRD4 that controls the receptor structure. The number of repeats of a 48-bp segment varies between individuals, ranging from 2 to 11 repeats. Individuals with at least one allele of 7 or more repeats (7R+) are more likely to seek out new experiences, hence the 7R+ allele is known as the "wanderlust gene."
Dopamine is a neurotransmitter in the brain that gives us feelings of reward and pleasure. The dopamine receptor D4 (encoded by the DRD4 gene) binds dopamine and transmits the signal into the cells. The 7R+ version of the DRD4 gene results in a receptor that binds dopamine less efficiently, compared to the common 4-repeat (4R) version, therefore transmitting reduced levels of signals in the brain. Individuals with the longer versions of DRD4 (7R+), therefore require higher levels of dopamine to achieve the same "good feeling" affects of dopamine.