Chimerism: what is it?  Chimerism is when fraternal twins fuse together while still in utero, resulting in an organism with two sets of DNA. It doesn't occur often, and both equines and people can be chimeras. 

Results of chimerism? For horses most commonly it'll be unusual splashes of color;however sometimes bi-colored eyes;abnormal hair growth and brindle occurs. In the case of chimeras non of their genetic abnormalities are hereditary. They are one of a kind. This doesn't occur often it is quite rare.  

Brindle horses?  

Yes, you've met brindle pittbulls and boxers,but how about a horse?  Nobody is sure how a horse comes out brindle. They just are. 

What is a brindle horse?  A horse with an unusual pattern of dark, vertical lines on a lighter - colored coat. It's quite rare, occuring rarely. According to Dr. Phillip Sponenberg, who wrote a book on equine genetics,  "brindle seems to require sooty black countershading for its expression;and recognizes sootiness into vertical striping instead of a unique form of sprinkling of hairs." 

Brindle can come in the form of white stripes on a dark coat, but usually it will not. Should that occur it isn't inheritable or able to be passed on to any offspring. Brindle in the form of chimerism isn't hereditary and cannot be passed down to any off spring. Brindle that is able to passed down is a skin condition that causes lesions. Although breedable, it isn't desired.

I'm still learning about brindling and chimerism so This might not be as accurate as a website, but I found it very interesting.