H T G 1 0
The locus HTG10 on Chromosome 21 is the location of both cream and pearl dilution mutations. Because there are only two alleles for each gene, that means a horse can be homozygous for one or heterozygous for both, but not homozygous for both.
C R E A M
Cream is an incomplete dominant, meaning that it dilutes to different extents depending on its zygosity. A single cream allele does not dilute black pigment, but it does affect red pigment. Single cream dilution on base coats are buckskin, smoky black, and palomino.
Buckskins are classically seen as golden with black points. Their phenotype can vary dramatically from very pale (sometimes called "buttermilk") to extremely dark, sometimes appearing undiluted or even black. Buckskins do not have dorsal stripes without the addition of other genes, whether they are known or not.
Smoky black has the same range of color as undiluted black. Some people say that there are ways to visually tell the difference, such as cream inside the ears of smoky black foals, but these are falsehoods. The only ways to tell a horse is smoky black vs undiluted black are if the horse has a double cream parent or by color testing.
Palomino is a single cream allele on a red base. They sport a golden coat with a cream-colored mane and tail. They can also range in shade from very light to very dark. Sometimes they can be mistaken for flaxen undiluted reds. Generally a palomino will have a less orangey or red undertone to the coat.
Buckskins are classically seen as golden with black points. Their phenotype can vary dramatically from very pale (sometimes called "buttermilk") to extremely dark, sometimes appearing undiluted or even black. Buckskins do not have dorsal stripes without the addition of other genes, whether they are known or not.
Smoky black has the same range of color as undiluted black. Some people say that there are ways to visually tell the difference, such as cream inside the ears of smoky black foals, but these are falsehoods. The only ways to tell a horse is smoky black vs undiluted black are if the horse has a double cream parent or by color testing.
Palomino is a single cream allele on a red base. They sport a golden coat with a cream-colored mane and tail. They can also range in shade from very light to very dark. Sometimes they can be mistaken for flaxen undiluted reds. Generally a palomino will have a less orangey or red undertone to the coat.
E_ A_ nCr and E_ aa nCr and ee nCr
Two cream alleles affect both black and red pigment equally and it can be virtually impossible to distinguish the three double cream dilutes from each other by simply looking at them. They all have overlapping phenotypes and look nearly identical. A second cream allele dilutes black skin to a pigmented pink and brown eyes to a baby blue or green. The coat is very pale. Bay with two cream alleles is perlino, black with two cream alleles is smoky cream, and red with two cream alleles is cremello.
E_ A_ CrCr or E_ aa CrCr or ee CrCr
P E A R L
Pearl is a recessive mutation on the HTG10 locus. It can only be seen affecting the coat when it is heterozygous with a cream allele or when it is homozygous recessive. Pearl has also been called the Barlink factor. When paired with cream, it dilutes sort of between single and double cream. When homozygous recessive, the coats ends up with a sort of apricot-ish tone.
E_ A_ Crprl or E_ aa Crprl or ee Crprl
E_ A_ prlprl or E_ aa prlprl or ee prlprl
E_ A_ prlprl or E_ aa prlprl or ee prlprl