the word is still out on brindle, still inconclusive as to whether it is an inheritable color pattern or chimera. I suspect both! Here is info from the web, the first from sponenburg, the foremost color expert...
According to Dr. Philip Sponenberg, BRINDLE is a unique gene that acts by REORGANIZING the COUNTER-SHADING caused by the SOOTY GENE into brindle strips. Because the striping patterns are similar to dun, it is sometimes confused with dun, especially in minimally brindle animals. For a long time, brindle was considered to be a form of dun. For a more thorough exploration of brindle, see Sharon Batteatte's Brindle Horse Website So far, Brindle has evaded breeders' attempts to breed for it. May '00 Information on Brenda Batty Atty (IBHA), and evidence for a brindle gene from her production records. Discussion of Phenotype (outward appearance) vs Genotype (actual genetic composition). Some brindle patterns seem to be the result of Chimerism (Mar '00), while others may be the result of a brindle gene (this month). A Brindled 2005 (2yr old) stallion shown at the top of the page has just come up for sale. His name is Mr Silver Poco Pine (Pedigree). The current owner says she bought him for a western/english pleasure prospect, and was originally planning to geld him. I suggested he should be test bred to some mares before gelding, to see if he has one of the inheritable types of brindle patterns. However, the owner has decided to sell him for $5,000 OBO. You can contact the owner, Melanie Lawson for more details. Brindle horses also have texturing in their coat, similar to that seen in some Appaloosa horses. The pattern seems to be inheritable, especially in terms of coat texturing, but the expression of the darker or more intense pigment to make the pattern visible is highly variable, and even varies with individual horses seasonally / yearly. Sometimes the pattern seems to be composed of dark hair (black or brown), sometimes of white hair (roan or gray). Information collected since 1990 on Brindle horses is now shedding some light on the Brindle pattern. It now appears there may be two ways in which a Brindle phenotype (outward appearance) can occur. In some horses, the pattern has not been inheritable, pointing to a possible mosaic or chimeric origin, such as seen in tortoiseshell cats. In other horses, the pattern has been shown to be inheritable. However, there could be several genes involved, producing similar patterns (much as pinto/paint spotting can result from several different genes).
