homozygous question

To be homozygous black, does the horse's parents have to both be black? My mare is black while her dam is also black & her sire chestnut tobiano so would that automatically make her heterozygous black or can she be homozygous black without both parents being black? My 2nd question is does that apply with patterns too, like tobiano? Thanks

All base color rules apply regardless of pattern.

Horses can be homozyous black without two black parents, but they have to both be black-based (bay, perlino, dun, buckskin, etc.). Your mare, with a chestnut parent, would have to be heterozygous black, as chestnut horses are homozygous red by definition and do not carry a black gene to pass on.

So without a genetic test it's certain my mare is heterozygous black? Thanks

Given her parentage, yes.

Yup, as Bubba said. A chestnut horse only has red genes to pass to it's foals. To be homozygous black, a horse needs to get a black gene from each parent.

Thank you both for the replies!
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