I have recently been reading the Horus Heresy novel 'Thousand Sons,' and have played through several different 'Dawn of War' games - a gaming friend told me this week that it is strongly hinted that the Blood Ravens gene seed is descended from the Thousand Sons legion. The chapter has no records of its founding roots, and this seems to have been shrouded in secrecy.
I wondered what anyone out there knew about this, and whether or not there were any other chapters that might have suspect gene seed, either taken from stored gene seed taken during the Great Crusade from legions that then subsequently turned traitor, or from some other defective batch. There have certainly been many examples of great swathes of certain chapters turning to Chaos. In another sense, this kind of 'experimentation' on the part of (presumably) the High Lords of Terra, must have a reason - it could form an interesting plot device within Deathwatch games perhaps?