Roan Calculators

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Roan is a coat color pattern in which white hairs are intermixed throughout a base coat color (bay, chestnut, or black) on the body, while the head and lower legs retain the base color. In cattle, roan results from the interaction of red and white alleles at the SILV locus — roan is produced when a calf inherits one red allele and one white allele (codominant inheritance). In horses, roan is inherited as an autosomal dominant trait — one copy of the Rn allele produces roan; homozygous (RnRn) is believed to be embryonic lethal. Dog roan patterns follow similar dominant or codominant mechanisms depending on the breed.

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Roan in Cattle (Shorthorn)

Shorthorn cattle coat color: Red (RR), White (WW), Roan (RW) — codominant. RW individuals have an even intermixing of red and white hairs. Cross: Red × White → all roan offspring. Roan × Roan → 1 Red : 2 Roan : 1 White (1:2:1 ratio). This is a classic example of codominance — neither allele is completely dominant.

Roan in Horses

Roan is an autosomal incomplete dominant trait in horses (Rn locus, chromosome 3). Rn/rn (heterozygote) = roan: white hairs mixed with base color on body; head and extremities retain base color. rn/rn = non-roan: no white mixing. Rn/Rn (homozygous): believed to cause embryonic lethality — no homozygous roan horses are confirmed, and roan × roan crosses produce fewer roans than expected. Unlike gray: roan is present from birth; gray horses darken at birth and gradually turn white over years.

Distinguishing Roan from Gray

Roan: white hairs present at birth; spares head and lower legs; does not progress. Gray: born with solid colored coat; white hairs develop with age; affects entire body including head. Dapple: circular lighter patches; may be confused with roan.

Glossary

Roan
A coat color pattern with white hairs intermixed throughout a base color on the body; stable from birth; spares the head and lower legs; inherited as codominant in cattle and autosomal dominant in horses.
Codominance
Both alleles are expressed simultaneously in the heterozygote; neither is dominant; roan Shorthorn cattle (RW) = both red (RR) and white (WW) alleles expressed; produces 1:2:1 ratio in F2 cross.
Rn Locus
The horse roan gene on chromosome 3; Rn/rn = roan; rn/rn = non-roan; Rn/Rn may be embryonic lethal; all roan horses are thought to be heterozygotes.

Frequently Asked Questions

Roan: a coat pattern with white hairs evenly intermixed throughout a base color (bay, chestnut, or black/blue) on the body, while the head, mane, tail, and lower legs retain the base color without white mixing. Roan is present at birth and does not change significantly with age. Gray: a progressive depigmentation pattern in which white hairs gradually replace colored hairs over months and years — horses may be born with a colored coat and become entirely white by middle age. The gray gene (STX17) works differently from roan (Rn). Key difference: roan spares the head; gray affects the entire body including the head.

In Shorthorn cattle, coat color at the SILV (Silver) locus is codominant: RR = red coat; WW = white coat; RW = roan (even mixture of red and white hairs). Crosses: Red × White (RR × WW) → all roan (RW). Roan × Roan (RW × RW) → 1/4 Red (RR) : 2/4 Roan (RW) : 1/4 White (WW) = 1:2:1 phenotype ratio. This is the textbook example of codominance because both alleles are expressed simultaneously in the heterozygote, rather than one being dominant over the other.

In horses, roan is controlled by the Rn (Roan) locus on chromosome 3. Inheritance is autosomal, and roan appears to be dominant (one copy produces roan phenotype) with homozygosity possibly lethal: Rn/rn (heterozygote) = classic roan: white hairs on body; full base color on head and legs. rn/rn = non-roan. Rn/Rn (homozygous): suspected embryonic lethality — confirmed homozygous roan horses have not been documented. Roan × roan crosses produce fewer roan foals than expected from a 3:1 ratio → supports the lethal homozygote hypothesis. All existing roan horses are therefore believed to be heterozygotes.

Classic (true) roan: white hairs intermixed with any base color on the body; stable pattern that doesn't change seasonally much. Bay roan: base color is bay (brown body + black points) + white mixing. Blue roan: base color is black + white mixing → appears blue-gray on body. Red/strawberry roan: base color is chestnut + white mixing → pinkish/strawberry appearance. Rabicano: a different white hair pattern that only affects the flanks and base of tail; may be confused with roan; controlled by a different gene (Rb). Varnish roan (Appaloosa): a progressive roan-like pattern associated with the Appaloosa LP gene complex; dark spots over the face, limbs, and bony prominences persist while body lightens with age — unlike true roan.