Magical gene / ground and strong white

Marble Tobiano

Tobiano gone streaky and angular - hair-thin veins on a minimal horse, broad blocky zones on a heavily marked one, and nothing at all unless it is homozygous. A third allele carries the same marking worked in greys instead of white - dark where the pale form is light, and the same number of steps.

What it can come out as

Outcome	Carrying
Marble Tobiano	`Tmr/Tmr` · `Tmr/Tmc` · `Tmr/Tmk`
Black Marble Tobiano	`Tmk/Tmk` · `Tmk/Tmc` · `Tmk/n`
Coloured Marble Tobiano	`Tmc/Tmc`
Marble Tobiano carrier	`Tmr/n` · `Tmc/n`
Wild type	`n/n`

How each one is actually drawn - region by region, and the layers it is built from - is on the coding tab.

Crossing two of them

Finding one

About 1 in 893 wild horses is born showing this. That is the whole of the supply: catch one, or make one with the carrot below. Breeds set their own pools and a breed built around this gene will carry it far more often than the wild population does.

Wild pair	Shows as	How often
`Tmr/Tmr`	Marble Tobiano	0.08% — 1 in 1,250
`Tmr/Tmk`	Marble Tobiano	0.0053% — 1 in 18,751
`Tmr/Tmc`	Marble Tobiano	0.0053% — 1 in 18,751
`Tmk/Tmk`	Black Marble Tobiano	0.0053% — 1 in 18,751
`Tmk/Tmc`	Black Marble Tobiano	0.0053% — 1 in 18,751
`Tmk/n`	Black Marble Tobiano	0.0053% — 1 in 18,751
`Tmc/Tmc`	Coloured Marble Tobiano	0.0053% — 1 in 18,751
`n/n`	Wild type	99.888%

Its gene carrot

The file

common/src/main/resources/horsegenetics/genes/marble_tobiano.json — a data-driven gene, not a Java class. It is listed in the index.json beside it and registered by Genes' class initialiser at startup.

Key	`horsegenetics.marble_tobiano`
Phase	magical — it adds signed colour in phase 3, after the pigment has resolved
Priority	205 — where it sits in the one `(priority, key)` paint order
Alleles	`Tmr` · `Tmk` · `Tmc` · `n`
Varies per horse	5 values drawn once off the expressing allele copy, so a foal that inherits the copy inherits the look
Built from	CENTERLINE, STROKES, TOWARD

Why it is built this way

The black allele is the white one with the light taken out of it, and it sits one rung under white in the dominance series - so every combination that existed before it keeps the outcome it had, and only the pairs carrying Tmk are new. The re-toning is a mapping rather than a repaint: every achromatic target moves into the dark end of the scale keeping its order and its spacing, and every SATURATED one is left alone, because that colour is the gene rather than its lightness.

What it paints

Each outcome, described the way the gene file describes it, and then the layers that draw it in the order they are painted. The prose is the part a reader checks a bake against; the list underneath is what the engine actually did.

Marble Tobiano

A tobiano that never learned to make a round patch. At its most minimal it is a set of hair-thin white veins running vertically and diagonally down from the topline, translucent enough that the coat reads through them, with a narrow line down the face. At its most extensive it is blocky zones eight inches and more across, fully opaque, with sharp defined edges. In between it flows in body-contoured curves at a few inches wide. It only does this when homozygous; a single copy leaves a horse barely distinguishable from an ordinary one, which is how the whole thing stayed hidden for so long.

angular white running down from the topline — STROKES × CENTERLINE, painted with TOWARD

Black Marble Tobiano

The same marking as the white form with the light taken out of it: a single near-black tone.

angular white running down from the topline — STROKES × CENTERLINE, painted with TOWARD

Coloured Marble Tobiano

The same veining in a colour the line carries rather than in white. Fully recessive: it takes two copies, and a single copy beside the white allele shows white. It never gives blue eyes, whatever the white form does.

angular white running down from the topline, in colour — STROKES × CENTERLINE, painted with TOWARD

Marble Tobiano carrier

A single copy is not expressed - barely noticeable, and easily mistaken for an ordinary horse.

Paints nothing.

Wild type

No marbling.

Paints nothing.