brindle horses

the new issue of Equus featured a small spread on brindle colored horses. there is a lot of uncertainty of how the bridle color in horses occurs, and it looks as though that geneticists may have a clue. it turns out that a DNA test of a brindle stallion and a bridle mare showed that both were a genetic anomaly known as chimeric. chimerism is when two otherwise fraternal twins fuse in the very early stages of development causing an organism with two complete sets of DNA. and just like the calico cat with her random patches of color being indicative of which of the two x-linked colors are being expressed over that square inch of the body, it appears that the chimeric horse may express this as a brindle pattern.