Color Genetics

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After 20 years of breeding, we receive many questions about coat patterns.  Here is a very basic genetics lesson for determining if a horse will pass on the pinto gene or not.  Yes, the genetics of color coat patterns is the same in miniature horses as any other breed of horse. 

TT - Tobiano Homozygous - Tobiano coat pattern present - Will always produce the pinto coat pattern even when bred to a solid HCM War Paint's Fashionation - homozygous pinto miniature stallion  HCM War Paint's Fashionation - homozygous pinto miniature stallion 

The miniature horse above displays obvious "paw prints",

HCM Navajo's X-Caliber - homozygous pinto stallion

but a homozygous pinto doesn't always show the pattern so obviously. Note fewer prints on this homozygous miniature stallion.

nT - Tobiano Heterozygous - Tobiano coat pattern present -

X-Caliber's Little Navajo - heterozygous pinto miniature horse stallion 

nn - Homozygous Negative - no Tobiano coat pattern present

HCM Navajo's Balck Magic - homozygous pinto negative miniature stallions

This chart shows the possibilities of offspring when mating two horses:
 

 
nn - SOLID COLOR
nT - PINTO NOT HOMOZYGOUS
TT - HOMOZYGOUS PINTO

nn - SOLID COLOR
100% nn

50% nT
50% nn
100% nT
nT - PINTO NOT HOMOZYGOUS

50% nT
50% nn

 
25% TT
50% nT
25% nn

50% TT
50% nT
TT - HOMOZYGOUS PINTO
100% nT

50% TT
50% nT
100% TT

 Tobiano coat pattern is a desirable quality for many horse owners. Tobiano coat pattern is governed by a single dominant gene meaning that there only needs to be one copy of the gene (tobiano heterozygous-nT) for the tobiano coat pattern to be present. Homozygosity of the tobiano gene (TT-two copies of the tobiano gene) may show visual clues but only genetic testing will tell you this more conclusively that there is Tobiano homozygosity rather than heterozygosity. When there is no copy of the tobiano gene (homozygous negative-nn), the tobiano coat pattern is not possible.