Natural gene / phase 1

Manchado — white with islands in it

The rare Argentine pattern: broad, clean white over the topline with smooth rounded islands of the base colour left inside it, a mostly white tail, and a head, belly and lower legs that stay dark. Close to the inverse of a leopard — a leopard puts dark spots on a white horse; this leaves dark islands in a white field.

What it does

What to look for: broad clean white over the back and neck with smooth rounded islands of colour left inside it, a mostly white tail, and a head, belly and lower legs that stay dark.

It is roughly the reverse of a leopard: a leopard puts dark spots on a white horse, this leaves dark islands in a white field. It is rare.

Crossing two of them

This gene has no effect on the horse’s health.

Its gene carrot

Gene key: horsegenetics.manchado
Alleles: ma Ma
Outcomes: wild, manchado-carrier (silent), manchado
Shows when: ma/ma, and only then
Default allele: Ma
Priority: ManchadoGene.PRIORITY — with the white-spotting loci
Founders: carriers only — no wild horse is ever manchado
Deterministic: no when expressed
Epi draws: 2 × nextLong — the field seed and the island seed
Health: none

Unplayed

Covered by ManchadoGeneTest and the golden file, and eyeballed as side views beside a tobiano and a leopard. Not seen in a game. See verification §0-W.

Its own locus, deliberately

Manchado is not a leopard-complex modifier and not a KIT allele. It is not one of the mapped, commercially testable white-spotting patterns at all: the modern reviews catalogue KIT (tobiano, sabino, the dominant whites), MITF and PAX3 (splash), EDNRB (frame) and TRPM1 plus RFWD3 (leopard complex and PATN1), and manchado is in none of them.

A horse cannot be confirmed manchado by a white-pattern panel. It is identified phenotypically, by its shape — so filing it under an existing locus here would have been a claim nobody has earned, and would have turned it into “another Appaloosa setting” rather than the thing it is.

Why recessive

The long-standing proposal is a rare autosomal recessive, written ma. That is a hypothesis, not a validated locus, and the mod says so — but it is the one that explains the observations: the pattern turns up sporadically out of solid-looking parents across several Argentine populations (Criollo, polo ponies, Arabians, Hackneys, Thoroughbred-associated stock) without spreading the way a dominant pinto gene would, which is exactly what a rare allele carried into several registries by a founder effect looks like.

The competing ideas are somatic mosaicism — a change occurring after conception in some pigment-cell lineages rather than an inherited allele — and a transposable element. Neither is proven either. This is a modelled allele based on a suspected inheritance pattern, and the real cause is unresolved.

Carriers only in the wild

The founder table has no affected row at all: about one wild horse in eighty carries a copy and none of them shows it. The only way to see a manchado is to breed two carriers, which is the whole point of a pattern this rare and the reason the carrier gets its own wording in the gene browser. The same shape the health loci use, for a much happier reason.

The geometry

Manchado is identified by shape rather than by how much white there is, so the shape is what the gene draws.

Feature	How it is drawn
A dorsal white sheet over the back, crest, upper shoulder, upper barrel and croup	A height threshold on the barrel and the neck, with a low-frequency wander so the margin is not a level waterline.
A crisp margin	A deliberately narrow smoothstep. Manchado's white does not dissolve into roaning, and a soft edge here would draw a sabino.
Rounded islands of base colour inside the white	The same cellular field grey's dapples use, at a large cell size, subtracted from the white rather than painted over it — an island is base coat the white never reached.
A mostly white tail	Reported as a notable manchado feature even when the hind legs stay dark.
A dark head, belly, underside of neck and lower legs	Excluded outright.

The islands were slivers first

Which cells are islands was originally sampled at the cells' own frequency, so it varied inside each cell and cut it in half — the field came out as slivers rather than as ovals. It is sampled at a much lower frequency now, which picks island-rich and island-poor regions and leaves each oval whole. Worth recording because the symptom (a pattern that looks torn rather than round) reads like an art problem and was arithmetic.

Health

None. This is the white pattern about which least is known, and inventing a cost for it would be inventing a fact. Every other white locus in the mod carries something; this one carries nothing, and a manchado horse resolves to exactly the same body as a solid one.

What it is not

Pattern	How it differs
Sabino	Jagged, roaned margins, and white on the face and legs. Manchado's white is clean and opaque, and its face and legs are dark.
Tobiano	Large smooth patches crossing the spine, usually with white legs — but no rounded islands inside the white. That is the whole difference.
Splash	Comes up from below: white belly, tall leg white, a bald face, blue eyes. Manchado is top-down and its underside stays coloured.
Leopard complex	Does put colour inside white, but with mottled skin, striped hooves and white sclera, and as a dense cloud of small spots rather than a handful of large ovals.
Roan	Hair-by-hair mixing, not patch white.

ManchadoGeneTest asserts the geometry directly rather than describing it — that the white is dorsal, that the belly and legs are untouched, and that the coloured leftovers inside the field are runs rather than single texels, which is the measurable difference between an island and a fleck.

Tobiano Leopard complex KIT (sabino / dominant white) Rabicano

Source: common/genetics/genes/ManchadoGene.java