On another thread I mooted the idea that in my view the number of Iron Hands successors was likely to be in the region of 10-20 chapters that know of their ancestry, and perhaps another 5 who didn’t.
That was just plucking numbers out of the air, of course, but it got me thinking about the numbers of other loyalist chapters out there who carry the geneseed of the founding legions.
So while we’re plucking numbers out of the air, here are some vague ideas on the topic. Not canon, but based on canon:
Ultra Helix – 60% of marine chapters (600) carry Ultramarine geneseed, by far the most stable and mutation-free helix available.
Pugnus Helix – 15% of marine chapters (150) carry the Imperial Fist geneseed. This is a stable and reliable geneseed, but is regarded as slightly less efficacious than the ultra helix due to the loss of a small number of marine implants through mutation.
Umbra Helix – Around 10% of Marine Chapters (100) bear the geneseed of theDark Angels. This geneseed is largely mutation free and stable, and indeed would be used more widely if not for the Adeptus Terra’s suspicion of the insular and secretive Dark Angels, who wield what is regarded as undue influence over their successor chapters.
Fulmen Helix – 8% of marine chapters (80) use the White Scar geneseed, making it relatively popular. It is a stable geneseed with few mutations, but the chapters created by it are often regarded as fractious, warlike and occasionally politically uncontrollable.
The Helix Sanguine – about 3% of marine chapters (30) carry this helix, which was popular during earlier foundings due to the notable loyalty and dedication of the Blood Angels shown during the Horus Heresy. However, the geneseed has fallen out of favour due to clear instabilities, notably the “flaw” which causes a kind of violent psychosis. Later attempts during the cursed founding to rectify these have not been successful. Few later foundings utilise the helix sanguine.
Ferrum Helix – less than 1% of chapters (10) bear the Iron Hands’ geneseed, largely due to that chapter’s reluctance to allow foundings based upon their geneseed.
Canis Helix – the Space Wolves geneseed is another extremely rare helix, used in only around 0.3% of marine chapters overall. (3)
Nex Helix – Around 1% of chapters (10) bear the geneseed of the Raven Guard. The numbers of the Raven Guard were never high, and the slight cosmetic mutation caused by the geneseed causes them to be regarded with some suspicion by the Adeptus Terra, leading to relatively few successors.
Ignis Helix – There are no known Salamanders successors, partly due to the highly visible nature of the cosmetic mutation which afflicts the Chapter.
Other sources – the remaining 1.7% of chapters draw (17) geneseed from other sources. These may be chimaeric in nature, with geneseed from different chapters merged together during a period of experimentation, or, more rarely, chapters which draw geneseed from forbidden or traitor geneseed. For example, the canon hints that the Blood Ravens draw their geneseed from the thousand sons. Alternatively, the geneseed may derive from existing loyalist chapters, but be so heavily modified that it is in effect totally new.
I would also say that around 10-20% of chapters out there don’t know what geneseed they carry, having lost records during the thousands of years of Imperial history.
These are only my figures, just setting out a general "feel" for the numbers involved. I would also say there's a lot of room for variance, at least 2 percentage points in either direction.
Any thoughts?