Board Thread:Warhammer 40k General Discussion/@comment-72.93.49.215-20140912200020/@comment-6078851-20140914161417

in regards to the term 'pure' gene-seed it should be made clear that there isn't a chapter currently in existence that has 100% pure gene-seed. one or two chapters may have had when they were created 10,000 years ago but the intervening years have caused biological blueprints to mutate, which is also known as evolution. however such mutation doesn't necassarily mean detrimental attributes, for example salamanders have evolved to have their black skin and red eyes but there's no negative effects to this, whereas space wolves do have detrimental attributes from their genetic mutation, namely the wulfen.

since the dark angels currently have the purest (least mutated) gene-seed it sounds logical, to me at least, that they've always had the least mutatable gene-seed: i believe that as they were the first to be created that emps got it spot-on on his first go and all subsequent creations didn't quite match up, genetically speaking, to the first - sort of like maybe he thought he would do the first one properly and the rest he tried to 'tweak' in one way or another which resulted in varying degrees of gene-seed stability.

the dark angels don't know of their gene-purity and only a small section of the inquisition do, and probably emps, but because of their secret ways and questionable battlefield actions the dark angels are one of the least trusted loyal chapters and as such the inquisition don't allow dark angel successors very often. and if the inquisition ever found out about the whole caliban schism they would almost certainly brand the D.A's as heretics.

the ultramarines have the greatest number of successors, and coupled with the fact that they are probably the single most trusted chapter it's widely believed in the imperium that they have the purest gene-seed.