User blog comment:Master Sima Yi/Assassinews 31-03-'15 — Assassin's Creed Chronicles announcement trailer/@comment-101.190.137.168-20150507012042/@comment-1153722-20150507075453

I think the Sage's appearance would only be their fenotype, not their real genotype. So I highly doubt it would 'break the familial line', and that their child would not contain any Sage DNA unless he's a Sage himself.