Pearl: a dilution that can stay hidden

What a visible Pearl coat can look like

On chestnut, two Pearl copies often give an even apricot tone in the body, mane and tail, with lighter skin. The base color and other modifiers affect the final appearance.

Pearl paired with Cream can give a much paler coat, pale skin and blue or greenish eyes, resembling a horse with two Cream copies. These clues help you compare appearances, but cannot establish which genetic combination the horse carries.

Sources for this explanation [1] · [2] · [3]

Understand the letters before the cross

Pearl and Cream are different versions, or alleles, of the same gene, scientifically called SLC45A2. Prl means Pearl; Cr means Cream. Here N stands for a reference version without either of those variants in the stated example. A Pearl-only laboratory result may use N more narrowly, so check its definitions.

N/Prl, without Cream, generally does not show Pearl dilution. The horse is a carrier and can pass Pearl on. Prl/Prl means two Pearl copies. Cr/Prl combines one Pearl and one Cream copy, making the horse a compound heterozygote. Pearl and Cream are versions of one gene, so a parent passes one of its versions to a foal rather than passing them as independent genes.

Sources for this explanation [1] · [2] · [3]

Example: two carriers with ordinary-looking coats

For two parents confirmed N/Prl, each can pass N or Prl. Every conception has a 25% chance of Prl/Prl, 50% of N/Prl and 25% of N/N. These describe this gene only and do not guarantee one particular outcome in four births.

A different cross, Cr/Prl with N/N, gives a 50% chance of Cr/N and 50% of Prl/N. None of those foals is Cr/Prl: the first parent passes one of its two versions, not both.

Sources for this explanation [1] · [2] · [3]

What testing needs to cover

Independent studies identified the DNA change responsible for Pearl in 2019. Read the Pearl result alongside Cream, especially for a very pale horse or a parent that shows no dilution. Some laboratories report the variants separately, so you need to consider the results together.

A negative Pearl test excludes the tested variant. It does not exclude other lightening variants of SLC45A2 or other genetic causes of a pale coat.

Sources for this explanation [1] · [2] · [3]

Where the explanations come from

Laboratory resources explain which variants are tested and how to read their results. Research papers describe the evidence, discoveries and remaining uncertainties. Each article links its explanations to the relevant sources. Published titles stay in their original language so you can find the exact work.

1. 1 · Laboratory explanation

   UC Davis VGL — Pearl

2. 2 · Research paper

   Holl et al. (2019) — SLC45A2 variants, pearl and sunshine

3. 3 · Research paper

   Sevane et al. (2019) — Molecular evidence for pearl dilution