After continually narrowing their search, they eventually found one gene that seemed to make the difference. Called SLC45A2, the gene appears in several species, including humans. In people, variations in the gene are associated with light skin color in modern Europeans and with one type of albinism people get. In mice, horses, chickens and medaka fish, variations in SLC45A2 are associated with lighter skin or fur. In certain horses and chickens, mutations in SLC45A2 make the animals unable to make yellow-orange pigment, but still able to make black-brown pigment, just like white tigers.