I think he means Homozygous. This means that their genes are dominant. Meaning that what ever they are bred they will be passed on to their off spring.

Example: A tobiano patterned horse bred to a solid horse and the foal is tobiano there is a good chance that the tobiano patterned horse is homozygous. The only way to know for sure if a horse is homozygous is to have them DNA tested. Some horses are considered homozygous for a certain trait if they pass it on over 95% of the time.

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