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This includes all 18 legions, not just standard loyalist. Loyalist seem to have more defect and mutation compare to the traitors. I could be wrong, because except for the DG and TS, the rest of traitor legions do not have high defect and mutation compare to the traitors. I've never heard any defect or high mutations amongst the traitors (EC, WE, WB, IW, NL, BL, AL), heck the EC had the most pure and stable gene-seed out of all legions thanks to Fulgrim's genotype. I've never seen anything official released by GW stating how much % defect and mutation did the traitors had. From my personal view I can only assume they had between 10-20% chances of deficiency (not counting the EC). My view and statement is that EC had the most stable gene-seed with the lowest deficiency, below 10%, followed by the DA and Ultramarines with 10% deficiency. And how the list goes on, I don't know I cannot rank them, that's why I'm asking here.

If you look at the Legions with the largest numbers you get an idea of which ones had the most stable geneseed.

For the Loyalist Legions those with the most stable (i.e. lack of mutation and ability to graft well to implanted Aspirants) were the Ultramarines, Imperial Fists, and Dark Angels. Unsurprisingly these are also the Legions that managed to split fairly well during the Scouring to form a fair few Successors while also being often used sources for creating newer Chapters.
The Blood Angels, however, had the most effective geneseed of any Legion. The 9th could take the most mutated baseline human and turn them into an angelic creature. It's what allowed the 9th Legion to rapidly expand during the Unification Wars despite being sent into the worst radzones on Terra and it's what allows the current Blood Angels Chapter to recruit from the wastelands of Baal.

For the Traitor Legions (prior to Chaosification of course) we have the Iron Warriors, Sons of Horus/Luna Wolves, World Eaters, and Word Bearers. The Iron Warriors' geneseed especially was particularly adaptable to an Aspirants genetics which meant the Legion was able to rapidly induct new Astartes with a very low failure rate. The Emperor's Children might have been a stable Legion but the advent of the Blight created by the Selenite Genecult caused massive and irreparable damage to their geneseed stocks. Only the rediscovery of Fulgrim allowed the Legion to create new, untainted geneseed.

We don't really know a whole lot but it is a fact that induction methods were far more advanced during the Great Crusade and Heresy than after. Legions could recruit entire Chapters in one go because they had pure sources of Primarch DNA to call upon. With the exception of the Thousand Sons, none of the Legions really suffered even if they had a genetic abnormality.
The long and short is the Legions were largely stable across the board with a very small number of exceptions but culture (like with the Salamanders and Raven Guard) or tactics (Death Guard and White Scars) meant that some were just smaller than others.

 Gert wrote:
If you look at the Legions with the largest numbers you get an idea of which ones had the most stable geneseed.

For the Loyalist Legions those with the most stable (i.e. lack of mutation and ability to graft well to implanted Aspirants) were the Ultramarines, Imperial Fists, and Dark Angels.

I think the Ultras have the most successor chapters among the loyalists, in large part because of their genetic stability. That's why they were once regarded as "vanilla" because they were the de facto baseline for all Imperial marines.

17 confirmed second founding Successors and 53 total confirmed Successors by the Ultima Founding.

Dark Angel Geneseed is noted to be particularly stable, at least the equal of Ultramarine.

 Gert wrote:
17 confirmed second founding Successors and 53 total confirmed Successors by the Ultima Founding.

I am fairly confident there was also some old lore that estimated over half of all Marine chapters were Ultramarines successors by the 41st Millennium.

I'd have to go digging, but it is likely to be Index Astartes or Codex Astartes.

I was under the impression that Alpha Legion geneseed was considered especially stable. Though maybe that's just in the context of the 41st millennium where much of the AL have spent their time in realspace instead of the Eye.

Lexicanum has this nice image, from the Deathwatch RPG:


I am pretty sure I have seen the same table in other sources. Only covers loyalist geneseed.

It also has the >50% Ultramarines successors figure- according to the citation, this is from Codex: Ultramarines (2nd edition).

Well with 100 supposed Chapters and 53 confirmed with I think two confirmed destroyed, we're still within reason for half.
That Salamanders being 90% is a weird one. Maybe some attempted justification for a lack of Successors and a small Chapter prior to the addition of the cultural aspect?

 Haighus wrote:
Lexicanum has this nice image, from the Deathwatch RPG:


I am pretty sure I have seen the same table in other sources. Only covers loyalist geneseed.

It also has the >50% Ultramarines successors figure- according to the citation, this is from Codex: Ultramarines (2nd edition).

90% chance of mutation for salamanders sounds bad but the mutation is always the same, the pitch black skin. Therefore I would say it is a stable as the ultramarines as it is providing just as consistent results.

The way I have read the lore, the release order or the legions reflected the stability of the gene seed but also the quality of the process of creating the astartes. So dark angles had a very stable and usable gene seed but by the time they got to alpha legion they were much better at creating consistency in the marines. However I suppose all marines are made equal now. And that’s not suggesting that alpha legion has the most unstable gene seed but considering the anomaly of the twins and the soul sharing properties between alparius omegon and seemingly the rest of the legion may indicate that from a scientific perspective the alpha legion gene seed was the hardest to work with.

I’d also suggest that that fact that all alpha legion marines look almost the same if not identical is an indication of the stability of the gene seed and the quality of the manufacturing process


Automatically Appended Next Post:
I’d also guess that the pure OG gene seed that Fabius obtained from Trazyn was very stable as it was taken from a primarch and kept in stasis and not exposed to the blight that the rest of the EC stock was exposed to. I think the only notable mutation was the white hair

The geneseed Fabius traded was specifically from before the Blight affected the 3rd.

 Gert wrote:
Well with 100 supposed Chapters and 53 confirmed with I think two confirmed destroyed, we're still within reason for half.
That Salamanders being 90% is a weird one. Maybe some attempted justification for a lack of Successors and a small Chapter prior to the addition of the cultural aspect?

Depends how you define deficiency.

Coal black skin and red eyes may seem broadly cosmetic, but to The Imperium, it’s still a mutation.


Automatically Appended Next Post:

 Haighus wrote:

 Gert wrote:
17 confirmed second founding Successors and 53 total confirmed Successors by the Ultima Founding.

I am fairly confident there was also some old lore that estimated over half of all Marine chapters were Ultramarines successors by the 41st Millennium.

I'd have to go digging, but it is likely to be Index Astartes or Codex Astartes.

Sounds about right - though that includes Chapters who aren’t sure who their Primarch is/was if memory serves?

According to Index Astartes 2 the 8th Legion has the lowest instance of mutation among the Traitor Legions in the current time-line:

The gene-seed of the Night Lords appears to be surprisingly pure. In fact, of all the Chaos Space Marine Legions, the Night Lords seem to bear the least evidence of mutation. This is perhaps due to a stable gene-seed stock, perhaps due to the fact they rarely associate themselves with a particular Chaos power for any length of time.

Index Astartes 2: page 27

Not sure how that compares to the various loyalist chapters.

 Gert wrote:
If you look at the Legions with the largest numbers you get an idea of which ones had the most stable geneseed.

Except people here have wrong idea. Having stable geneseed is all well and good, but it's meaningless if it was poor to begin with. Let's take Ultramarines - they have "same" stability as IF and DA, but their geneseed works perfectly, while IF have multiple damaged/missing organs making their quality way lower to begin with even if they are supposedly 'stable'. Dark Angels are superficially all right but they get paranoia/secretiveness in the genetic package (plus less overall efficiency than UM) so the High Lords were really reluctant to use theirs for millennia (and all the 'friendly fire' and hasty withdrawals DA did on the side really didn't help their case).

That's why UM were responsible for close to 65% of all chapters - high diversity and purity meant High Lords could always find the UM descendant with culture they needed and have it split into two and work out of the box in every case, while being sufficiently removed from Ultramar to not be in any risk of colluding with Macragge. This calculus only changed when a superhuman who all UM were compelled to follow on genetic level arrived on the scene but until then, if you wanted good quality chapter that obeyed orders instead of ignoring them for insane reasons like the other 8 loyalists UM were really the only possible quality pick.

 Gadzilla666 wrote:

The gene-seed of the Night Lords appears to be surprisingly pure. In fact, of all the Chaos Space Marine Legions, the Night Lords seem to bear the least evidence of mutation. This is perhaps due to a stable gene-seed stock, perhaps due to the fact they rarely associate themselves with a particular Chaos power for any length of time.

Index Astartes 2: page 27

Least evidence of mutation among the CSM is like stating water straight from gas station toilet is cleaner than one from industrial sewage plant. It's kinda true but it still compares poorly to tap water. And that is before you remember NL had multiple mutations/organ deficiencies to begin with (plus paranoia complex even worse than DA one) even in 30K making other CSM look even worse if that is supposed to be a hard bar to clear.

 Haighus wrote:

 Gert wrote:
17 confirmed second founding Successors and 53 total confirmed Successors by the Ultima Founding.

I am fairly confident there was also some old lore that estimated over half of all Marine chapters were Ultramarines successors by the 41st Millennium.

I'd have to go digging, but it is likely to be Index Astartes or Codex Astartes.

I think that might have been 2nd edition.

Headcount of a given Legion is also based on how willingly their Primarch spent their Legionnaire’s lives.

Iron Warriors and World Eaters weren’t exactly cautious about such things, yet still maintained their numbers via induction.

So guess it’s possibly more accurate to look at how well a given Legion maintained and grew headcount compared to casualties.

 Irbis wrote:
Except people here have wrong idea. Having stable geneseed is all well and good, but it's meaningless if it was poor to begin with. Let's take Ultramarines - they have "same" stability as IF and DA, but their geneseed works perfectly, while IF have multiple damaged/missing organs making their quality way lower to begin with even if they are supposedly 'stable'. Dark Angels are superficially all right but they get paranoia/secretiveness in the genetic package (plus less overall efficiency than UM) so the High Lords were really reluctant to use theirs for millennia (and all the 'friendly fire' and hasty withdrawals DA did on the side really didn't help their case).

Just to counter some of the points brought up here, the Dark Angels' secretiveness is not genetic but cultural. They are secretive because they choose to be and propagate that choice through their Successors with whom they share a bond closer than any other group of Chapters. Dark Angel's geneseed is perhaps even the most genetically pure of all, which is why it was confusing that they were used as a source by the High Lords when a new founding was initiated.
But the High Lords didn't trust the Dark Angels due to their secretive and often abrasive manner towards Imperial authority, and as such would choose to use other lineages when founding new Chapters, ones that had proven to be more trustworthy and willing to cooperate with Imperial authority such as the Ultramarines and Blood Angels.

That's why UM were responsible for close to 65% of all chapters - high diversity and purity meant High Lords could always find the UM descendant with culture they needed and have it split into two and work out of the box in every case, while being sufficiently removed from Ultramar to not be in any risk of colluding with Macragge. This calculus only changed when a superhuman who all UM were compelled to follow on genetic level arrived on the scene but until then, if you wanted good quality chapter that obeyed orders instead of ignoring them for insane reasons like the other 8 loyalists UM were really the only possible quality pick.

The Ultramarines had the largest number of Second Founding Successors because they had the numbers to do so. Every other Legion had taken brutal losses throughout the Heresy leaving the Ultramarines and Guilliman in the prime position to take charge of crafting the new order. They started off very strong and that just continued. If the Imperial Fists or Dark Angels had been in the same situation (i.e. not having a battered Legion or a missing Primarch) then they would have come closer to matching the Ultramarines in terms of Successors.
Being close to or far away from Maccrage also doesn't mean anything when it comes to loyalty to the Imperium or High Lords. The Emperor's Spears were given territory far from Maccrage but didn't regard the Imperium with any greater loyalty. In fact, they came to be scornful of any outside influence be it Astartes or Imperial thanks to the culture of their new homeworld.

I’d also suggest the High Lords don’t particularly care whether a given Geneseed retains a given organ, so much as it has a high chance of churning out a Space Marine, rather than a failed aspirant.

That’s because Geneseed is finite, and a bit of a pain to replace. Though I’m still not entirely convinced post-mortem harvesting is the only way it’s obtained, as I can’t see, and am not aware of, any reason why once a Progenoid Gland has matured it wouldn’t be removed aboard ship between actions. Unless of course the Progenoid Gland serves other purposes -perhaps aiding in keeping the various hormones and other chemical goodness balanced?

Progenoids produce multiple organs. When one matures it can be harvested from the Astartes by Apothecaries and placed in the gene-vaults whereupon a new organ will begin to grow. Its how Chapters keep up their stores and why it's such a blow if an Astartes dies without their geneseed being recovered because it is not one lost warrior but two.

Do you have a citation for Progenoids regrowing after life extraction?

I ask because it’s something I speculated on a while back, and was pretty roundly shot down on. So if there’s a source for that I’m interested to read it

Might have been a Codex but not sure. Lex hasn't got the citation but I'm fairly certain I read it somewhere else first. Then again I might have just read it on another wiki. I only have the 9th Ed Codex and that is very sparse on the background side.

Even if it doesn’t spontaneously regenerate, given the organs are cultivated from Geneseed, I can see immature Progenoid being popped in to replace it, as presumably one can cultivate such fairly readily, if not outright clone it? Depending on Chapter of course.

 Mad Doc Grotsnik wrote:
I’d also suggest the High Lords don’t particularly care whether a given Geneseed retains a given organ, so much as it has a high chance of churning out a Space Marine, rather than a failed aspirant.

That’s because Geneseed is finite, and a bit of a pain to replace. Though I’m still not entirely convinced post-mortem harvesting is the only way it’s obtained, as I can’t see, and am not aware of, any reason why once a Progenoid Gland has matured it wouldn’t be removed aboard ship between actions. Unless of course the Progenoid Gland serves other purposes -perhaps aiding in keeping the various hormones and other chemical goodness balanced?

I do not know where it is from, but there are two points to consider:

1. The extraction of one of the glands in a live subject requires extensive surgery and prolonged rest after that if the subject is to remain viable later - with dead or near-dead subjects you can of course use rougher methods.

2. There seems to be some psychic or gene-mnemonic effect, as a gland gets 'better' the longer it remains in its host - implants that derive from an especially mature specimen have better chances of sucess in implantation, and are said to impart some of the personality of the erstwhile owner to the recipient, including some of his martial prowess.

For this reason, one gland is usually removed as soon as it has matured, while the other remains with the bearer ideally until his death.

As i said, i do not remember where i read that, but i suspect it was in one of the source books for the Deatwatch game.

Tsagualsa wrote:

 Mad Doc Grotsnik wrote:
I’d also suggest the High Lords don’t particularly care whether a given Geneseed retains a given organ, so much as it has a high chance of churning out a Space Marine, rather than a failed aspirant.

That’s because Geneseed is finite, and a bit of a pain to replace. Though I’m still not entirely convinced post-mortem harvesting is the only way it’s obtained, as I can’t see, and am not aware of, any reason why once a Progenoid Gland has matured it wouldn’t be removed aboard ship between actions. Unless of course the Progenoid Gland serves other purposes -perhaps aiding in keeping the various hormones and other chemical goodness balanced?

I do not know where it is from, but there are two points to consider:

1. The extraction of one of the glands in a live subject requires extensive surgery and prolonged rest after that if the subject is to remain viable later - with dead or near-dead subjects you can of course use rougher methods.

2. There seems to be some psychic or gene-mnemonic effect, as a gland gets 'better' the longer it remains in its host - implants that derive from an especially mature specimen have better chances of sucess in implantation, and are said to impart some of the personality of the erstwhile owner to the recipient, including some of his martial prowess.

For this reason, one gland is usually removed as soon as it has matured, while the other remains with the bearer ideally until his death.

As i said, i do not remember where i read that, but i suspect it was in one of the source books for the Deatwatch game.

The old IA Rites of Initiation article said much the same.

The earlier maturing progenoid generally gets removed on maturation, the other one generally stays in until death. The reasoning in that article was 1) it is apparently ’better’ somehow if left for longer; and 2) apparently it has a stabilising effect on the other organs that can mitigate any issues with the gene seed.

Obviously if you’re making a new chapter then you’re mass producing them in vat grown bodies which you junk as soon as they’re both matured, so that’s somewhat different.

@Irbis gave out the best answer on what a gene-seed is though.

Concerning the traitor legions, it seems we have little evidence, but we can see that they were the legions with the least defects and 0 mutations. And regarding the EC, what I was able to find on the Internet, for answers, is that Fulgrim was the purest out of all the Primarchs, it makes sense since Primarchs represent aspects of the Emperor. Fulgrim not only represents but his gene-seed is the closest to the Emperor, thus making him and his EC with the least deficiency amongst all 18 legions. Probably one of the best answers I've found on Reddit

Purity of gene-seed refers to the amount it has deviated from its original form, and the chances that it will

a) successfully create a Space Marine

and

b) have a mutation in it.

Fulgrims gene-seed was the most 'pure' as it had the fewest imperfections in it, and didn't degrade as much between subsequent generations of Astartes, as well as avoiding major mutations.

To put it one way, Astartes A gets a 100% pure gene-seed, astartes B 99% pure (1% higher chance of failure and mutation), C gets 98%, etc. But Emperors Child C, due to the purity of his gene-seed, is still above 99%, due to the resilience of the Fulgrim Genotype against genetic drift, degradation, and adulteration. That is one way to explain what is meant.

Note: The Blight virus that the EC got plagued by the Lunar cult is not inherent.

The traitor legions did not show any big defects like their loyalists, meaning that the traitors de-facto have the most stable gene-seeds.

I came up with a list, I'm a bit sleepy, so I could make mistakes:

1. EC (below 10%)
2. UM; BL; DA; IW; WE; AL; WB; NL (10%)
3. WS; RG; DG; IF; IH (20%)
4. BA (50%)
5. SW (75%)
6. Salamanders; TS (90%)

The TS gene-seed "defect". It's heavily implied that it's a Tzeentch problem and not a TS problem.

 Gert wrote:
If you look at the Legions with the largest numbers you get an idea of which ones had the most stable geneseed.

For the Loyalist Legions those with the most stable (i.e. lack of mutation and ability to graft well to implanted Aspirants) were the Ultramarines, Imperial Fists, and Dark Angels. Unsurprisingly these are also the Legions that managed to split fairly well during the Scouring to form a fair few Successors while also being often used sources for creating newer Chapters.
The Blood Angels, however, had the most effective geneseed of any Legion. The 9th could take the most mutated baseline human and turn them into an angelic creature. It's what allowed the 9th Legion to rapidly expand during the Unification Wars despite being sent into the worst radzones on Terra and it's what allows the current Blood Angels Chapter to recruit from the wastelands of Baal.

For the Traitor Legions (prior to Chaosification of course) we have the Iron Warriors, Sons of Horus/Luna Wolves, World Eaters, and Word Bearers. The Iron Warriors' geneseed especially was particularly adaptable to an Aspirants genetics which meant the Legion was able to rapidly induct new Astartes with a very low failure rate. The Emperor's Children might have been a stable Legion but the advent of the Blight created by the Selenite Genecult caused massive and irreparable damage to their geneseed stocks. Only the rediscovery of Fulgrim allowed the Legion to create new, untainted geneseed.

We don't really know a whole lot but it is a fact that induction methods were far more advanced during the Great Crusade and Heresy than after. Legions could recruit entire Chapters in one go because they had pure sources of Primarch DNA to call upon. With the exception of the Thousand Sons, none of the Legions really suffered even if they had a genetic abnormality.
The long and short is the Legions were largely stable across the board with a very small number of exceptions but culture (like with the Salamanders and Raven Guard) or tactics (Death Guard and White Scars) meant that some were just smaller than others.

I disagree, since the largest legions had the unknown legions absorbed and not due to purity of gene-seed. Also the IF have a lot of gene-seed failure.

The EC's reserves on Terra were corrupted by the Bight Virus used by the Selenar cult, a gene-cult on Luna. The disease is not inherent to their gene-seed like Red Thirst and the Wulfen. A few marines were implanted with the corrupted gene-seed, amongst them Fabius. On Fabius's orders all infected EC were killed.

 Wyldhunt wrote:
I was under the impression that Alpha Legion geneseed was considered especially stable. Though maybe that's just in the context of the 41st millennium where much of the AL have spent their time in realspace instead of the Eye.

 Gadzilla666 wrote:
According to Index Astartes 2 the 8th Legion has the lowest instance of mutation among the Traitor Legions in the current time-line:

The gene-seed of the Night Lords appears to be surprisingly pure. In fact, of all the Chaos Space Marine Legions, the Night Lords seem to bear the least evidence of mutation. This is perhaps due to a stable gene-seed stock, perhaps due to the fact they rarely associate themselves with a particular Chaos power for any length of time.

Index Astartes 2: page 27

Not sure how that compares to the various loyalist chapters.

I am not talking about corrupted gene-seed when I explicitly stated traitors, the current traitor CSM have their gene-seed corrupted by Warp AIDS, what I'm talking about is pre-heresy and post-heresy OG (untainted gene-seed). The traitor legions with the exception of the TS and DG, never showed any big mutation or defects unlike their loyalist counterparts.

The Blood Angels have the purest gene seed. Pure unadulterated BAMF Geneseed (Tm)

Pure 'whiny emo Twilight vampires kill your friends and loved ones, drink the blood of the tainted and impure and psychically vulnerable to influences from thousands of years ago' perhaps. But not 'BAMF'
They lost that when the ghoul legion met Sanguinius.

 F.E.A.R. wrote:
The TS gene-seed "defect". It's heavily implied that it's a Tzeentch problem and not a TS problem.

No, it isn't. The initial Flesh Change was a result of their shared DNA with Magnus and the use of their Psychic powers accelerated the curse. Magnus traded one of his eyes to a Warp entity (later revealed to be Tzeentch) in an attempt to cure the Flesh Change but it only reduced its severity. When the Thousand Sons fell to Chaos the Flesh Change returned stronger than before and encouraged Ahriman to conduct the Rubric.

I disagree, since the largest legions had the unknown legions absorbed and not due to purity of gene-seed.

You are conflating a few contradictory sources to make that argument.
The first source to indicate that the Lost Legions were absorbed by others is First Heretic where it is first said as a joke by one of Argel Tal's Word Bearers and it is regarded by Ingethel the Ascended as "insipid conjecture". It specifically is said in reference to the Ultramarines, who the Word Bearers have an undying hatred of. Hardly an unbiased source.
The only other source that suggests this is the novella The Chamber at the End of Memory where Malcador reveals that the Astartes of the Lost Legions were mind-wiped and "attuned to new circumstances". We can assume this means that they were sent to other Legions but it doesn't say which ones.
It is never confirmed where these Legionaries went or what, if any, Legions they were sent to.

Also the IF have a lot of gene-seed failure.

Have you got a source for this? I can't find anything to support this notion.

 Irbis wrote:

 Gadzilla666 wrote:

The gene-seed of the Night Lords appears to be surprisingly pure. In fact, of all the Chaos Space Marine Legions, the Night Lords seem to bear the least evidence of mutation. This is perhaps due to a stable gene-seed stock, perhaps due to the fact they rarely associate themselves with a particular Chaos power for any length of time.

Index Astartes 2: page 27

Least evidence of mutation among the CSM is like stating water straight from gas station toilet is cleaner than one from industrial sewage plant. It's kinda true but it still compares poorly to tap water. And that is before you remember NL had multiple mutations/organ deficiencies to begin with (plus paranoia complex even worse than DA one) even in 30K making other CSM look even worse if that is supposed to be a hard bar to clear.

Paranoia complex? Yeah sure, they've got that. But as Gert pointed out for the Dark Angels, that's a cultural problem, no a gene-seed problem. It's basically what happens when the vast majority of your aspirants are psychotic criminals/gangers to begin with, and then you "fast-track" them through the implantation process with minimal psycho-conditioning. You get super human criminals/gangers, because you didn't program the criminal/ganger behavior out of them. So, they stick with that culture.

As for the 8th Legion having "multiple mutations/organ deficiencies" to begin with: do you have a source for that? Because I've never seen it. All of the Night Lords implants work perfectly fine in the current time-line, so obviously they would have worked in the Heresy era. Same for mutations, as the majority of Legions had low instances of mutation in that time do to better methods and having access to their Primarchs. So, give me a source, or I'll just assume it's more of your "fan-fic" that you love throwing into your comments so much.

Voss wrote:
Pure 'whiny emo Twilight vampires kill your friends and loved ones, drink the blood of the tainted and impure and psychically vulnerable to influences from thousands of years ago' perhaps. But not 'BAMF'
They lost that when the ghoul legion met Sanguinius.

Seriously though, for a single bit, wasn't Sanguinius the MOST pure of all the primarchs? I thought he was literally considered flawless, or was that just his physical form? Also, we might also go out on a limb here and point out the greatest space marines come from BA stock. Even excluding Dante, Mephy is something of a singularly powerful entity that is unmatched by peers.