Equine linkage group II includes a number of genes. The first linkage was found between a blood type marker and tobiano white spotting in 1978. The same blood type marker, albumin, was linked to another blood protein called vitamin D-binding protein. In 1982, a linkage grouping was proposed, including three genes for serum proteins, and three for coat color: tobiano spotting, chestnut, and roan. Research since equine linkage group II was defined has identified the exact location of the tobiano allele and the chestnut allele. The region of the chromosome that harbors the roan gene is homologous to parts of chromosomes in other species that also control coat color, even some similar to roan. Presently, the KIT gene is the primary candidate gene for roan. While a chromosomal inversion of KIT causes tobiano white spotting, KIT also harbors one or more alleles responsible for sabino spotting, no fewer than eleven alleles responsible for dominant white spotting, and is thought to be a major contributor to many other forms of less distinctive white markings.