Originally Posted by Dreamcatcher Arabians
Since the sire is alive and overo, then he's got to be heterozygous.
This is not a valid assumption. "Overo" does not equal "frame". This is the EXACT reason why people with a sound genetic knowledge all advocate for the dumping of the word "overo". It is too vague, a catch-all term that really means "my horse isn't tobiano, and I can't work out what white pattern is there, and don't want to test, so I am just going to use this lazy, ambiguous word and hope no one notices".