Board Thread:Warhammer 40k General Discussion/@comment-58.178.141.62-20140405080514/@comment-217.115.146.100-20140408153933

as gene seed  is coded to a primarch and as the immune system of humans normally attacks foreign tissue (which is f.e. an issue with transplants, when your body receives auto immune blockers to  prevent it from attacking the new organ) you can be pretty sure that any chapter takes it's gene seed only from the basis of one primarch, as otherwise the organs would attack each other.

some far fetched hints are made at other chapters being based on traitor legions ( sons of antaeus f.e. though that hint is small) and  even if not saved, IOM had f.e. 70 loyal death guard, a couple of iron warriors and others.