Horses with the dominant "D" allele ("D/D" or "D/d" genotype) exhibit hypomelanism of the body coat, while "d/d" horses have otherwise intense, saturated coat colors. The mane, tail, head, legs, and primitive markings are not diluted. In some breeds, zygosity for "Dun" can be determined with an indirect DNA test. The "Dun" locus is TBX3 on equine chromosome 8. The molecular cause behind the dun coat colors is not entirely understood, but the dilution effect comes from the placement of pigment in only part of the hair. The associated coat colors were assigned to the "Dun" locus in 1974 by Stefan Adalsteinsson, separate from "Cream", with the presence of dun dilution indicated by the dominant "D" allele. The dominant "D" allele is relatively rare compared to the alternative "d" allele, and for this reason, the dominant allele is often treated as a mutation. However, the pervasive coat color among wild equids is in fact dun, and researchers from Darwin to modern day consider dun to be the wildtype state. An older non-dun mutation was found in 2015 and named non-dun 1. It creates primitive markings but does not dilute the base color, and is co-dominant with the more common non-dun 2 but recessive to dun. "Cream" is another one of the genes that control the saturation or dilution of pigment in the coat. "Cream" differs from "Dun" in that it affects the coat, skin, and eyes, and unlike "Dun", is dosage dependent rather than simple dominant. Furthermore, the effects on eumelanin and pheomelanin are not equal. Horses with the homozygous recessive genotype ("C/C") are not affected by cream. Heterozygotes ("CCr/C") have one cream allele and one wildtype non-cream allele. Such horses, sometimes called "single-dilutes", exhibit dilution red pigment in the coat, eyes, and skin to yellow or gold, while eumelanin is largely unaffected. Homozygotes ("CCr/CCr") have two cream alleles, and are sometimes called "double-dilutes." Homozygous creams exhibit strong dilution of both red and black pigment in the coat, eyes, and skin to ivory or cream.