Brindle and Brindle 1

What it looks like

Brindle describes vertical or irregular stripes of contrasting hair. Some horses mainly show differences in color; others also have differences in hair texture. In Brindle 1, hairs within the stripes may be unruly, and the pattern can change with the season. Distinguish a change in hair color from a change in the structure of the hair itself.

Sources for this explanation [1]

What happens biologically

Brindle 1, abbreviated BR1, is a particular variant in MBTPS2. This gene contains instructions used to make a protein; the cell first copies those instructions into messenger RNA. BR1 alters the way that working message is assembled. Because MBTPS2 is on the X chromosome, females with two X chromosomes and males with one X chromosome do not have the same possible combinations.

A different route to a brindle appearance is chimerism: genetically different cell populations originate from different embryos and coexist in one animal. Finding stripes therefore does not establish BR1, and inheritance of the known BR1 variant cannot explain every chimeric pattern.

Sources for this explanation [2]

Inheritance and DNA testing

A female with one BR1 copy usually shows striped coat texture and has a 50% chance of passing the variant to each foal. Females with two copies can have sparse manes and tails without the characteristic stripes. Males carrying BR1 also tend to have sparse manes and tails rather than the striped texture. The test targets this specific variant, and its interpretation must include sex.

A male passes his X chromosome to daughters and his Y chromosome to sons. For example, a BR1 male paired with a female tested without BR1 passes BR1 to all daughters, who receive one copy, and to no sons. That is different from a universal 50% rule for every striped horse.

Sources for this explanation [1]

Confusions, limits and health

A negative BR1 result does not explain every brindle-like appearance, and a photograph cannot confirm chimerism. A laboratory may need samples from different tissues to investigate whether genetically different cell populations are present. Dun bars on the legs, ordinary dapples and changes in hair texture have different meanings. Breeding predictions depend on the biological cause, so do not assume every striped coat comes from the same dominant color variant.

Sources for this explanation [1] · [2]

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 — Brindle coat texture

2. 2 · Research paper

   Murgiano et al. (2016) — An intronic MBTPS2 variant results in a splicing defect in horses with brindle coat texture