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A Neophyte undergoes the painful transformation into a Space Marine

The Progenoid Glands, also known as the Gene-Seed, are the 18th of the 19 genetically-engineered gene-seed organs implanted within an adolescent Space Marine Neophyte to create a new Astartes.

Every Space Marine has these organs, one implanted in the neck and another in the chest. The organs hormonally respond to the presence of the other Astartes gene-seed implants in the body by creating germ cells with DNA identical to that of those implants through a process very similar to cellular mitosis.

These germ cells grow and are stored in the Progenoid organs, much like sperm cells or egg cells are stored in the testes and ovaries of normal men and women. When properly cultured by the Apothecaries of a Space Marine Chapter, these germ cells can be gestated into each of the 19 gene-seed organs needed to create a new Space Marine.

Thus, for most Astartes, their Progenoid Glands represent the only form of reproduction they will ever know, though the DNA passed on will be that of their Primarch, not their own.

Mature Progenoid organs can be removed and new gene-seed implants artificially cultured from them. This is the only way new implants can be created, so a Chapter depends upon its existing Space Marines to create other Space Marines.

Five Terran years after implantation, the Progenoid Gland in the neck contains mature gene-seed and may be removed and its germ cells harvested, while the larger chest Progenoid is not considered ready for harvesting until 10 Terran years have passed.

The harvesting is normally done after an Astartes' death by an Apothecary, who carries a special attachment on the mobile medical field kit he carries on his arm known as a Narthecium. This attachment is called a Reductor and it is specifically used to extract both Progenoid Glands from the body of a slain Astartes so that his gene-seed can be used to replace the Chapter's loss, the only form of true immortality that Astartes will ever know.   

Just like normal human germ cells, exposure to high concentrations of ionizing radiation can effectively render a Space Marine "sterile" by destroying the germ cells within his Progenoids. Over the long millennia since the Space Marine Legions were first founded, a Space Marine Chapter's gene-seed can also mutate, producing new and hitherto-unknown physiological effects in that Chapter's Space Marines or simply becoming non-functional.

Repeated exposures to the corrupting Warp energies of Chaos can also cause mutation within the gene-seed. This is why every Chapter's gene-seed is required to be monitored for mutation and genetic purity by the Tech-priests of the Adeptus Mechanicus and why every Chapter is required to tithe 5% of its gene-seed stocks at regular intervals to the Mechanicus on Mars. This is done both to check for genetic purity and to be used to create new Space Marine Chapters if the High Lords of Terra call for a Space Marine Founding.

Chaos Space Marines

The Traitor Legions of Chaos Space Marines also all possess Progenoid Glands, which could originally be harvested to create new Astartes.

The problem is that their constant exposure to the corrupting energies of Chaos, particularly for those Traitor Legions that now live within the Eye of Terror where exposure to Chaos energies is constant and intense, often leads to the complete mutational degeneration of the gene-seed.

The problem has become so acute that many Heretic Astartes warbands now seek to raid Loyalist Space Marine gene-seed repositories so that they might be able to replenish their Legions' losses over the last 10,000 Terran years since the Horus Heresy.

Known Gene-Seed Flaws

Loyalist Chapters

Chapter Name Parent Chapter Known Mutations Summary
Blood Angels N/A N/A The Blood Angels and their Successor Chapters are a dying breed, for they suffer from a dreadful genetic Flaw. Some Blood Angels, it is said, are driven by a terrible deathseeking madness called the Black Rage, brought on by visions of the death of their Primarch. Others are afflicted by the Red Thirst, a craving for blood which some claim may be the first signs of corruption by Chaos.
Blood Drinkers Blood Angels N/A The Blood Drinkers' gene-seed, drawn from Sanguinius just like that of the Blood Angels, has further mutated, leading to a worsening of the Red Thirst Flaw in which the Blood Drinkers suffer an overriding thirst to ingest the blood of their enemies in order to stop the cravings. Unlike the Blood Angels and their other Successor Chapters, these cravings afflict the entire Chapter and not just those who fall to the Red Thirst. This has led to the development of Chapter-wide blood drinking rituals which both provided the Chapter with its name and keeps the blood-lust in check.
Blood Ravens Unknown The Blood Ravens can no longer experience true REM (rapid-eye movement) sleep and so they cannot dream, and after they are implanted with their gene-seed organs, they possess perfect recall of every event for the rest of their lives. Even though the Adeptus Mechanicus has tested the Blood Ravens' gene-seed for mutation or Chaos contamination at a substantially more frequent interval than that normally required, their gene-seed has consistently shown a high level of stability and purity. At the same time, it is unusual that it shows no consistent traits that could be used to link it to the genetic lineage of any of the Primarchs. Thus far, there has been little evidence of mutation, and nothing that points to their gene-seed as the source of the Blood Ravens' disproportionate number of psykers or the unusual potency of the psychic powers they exhibit.
Excoriators Imperial Fists This Chapter has lost the use of two of the special organs produced by the basic Astartes genetic template: the Betcher's Gland, which allows a Space Marine to produce poisonous/acidic spittle, and the Sus-an Membrane, which allows an Astartes to enter a state of suspended animation. The Excoriators believe themselves to be pure of heart but not of blood. As former members of the Imperial Fists Legion and now as a Chapter of their own, they are not alone in their experience of genetic deficiency. Like some of the First Founding Chapters and some of their Successors, the Excoriators also carry the flaws of their blood heritage. The Excoriators are afflicted by a genetic curse known as Dorn's Darkness. When Dorn's Darkness takes one of their number it might appear to the untrained eye as merely a wretched palsy: a slackness of the jaw, a tremor of the limb, a blankness of the eye. But those who survive it report the experience as a living nightmare, a sleeping wakefulness in which they relive the bottomless woe of Dorn’s most trying time—the grievous loss of the Emperor during the Battle of Terra. Like other Successor Chapters of the Imperial Fists, the Excoriators have a morbid fascination with pain and ritual scarring. They too, possess their own unique Chapter traditions. Most notable of these are the "Rites of Castigation" and "Donning Dorn’s Mantle," the latter of which involves ritual mortification of the flesh, particularly about the neck and shoulders.
Imperial Fists N/A This Chapter has lost the use of two of the special organs produced by the basic Astartes genetic template: the Betcher's Gland, which allows a Space Marine to produce poisonous/acidic spittle, and the Sus-an Membrane, which allows an Astartes to enter a state of suspended animation. The Imperial Fists' gene-seed is very stable and has never exhibited signs of mutation. Another peculiar and unexplained quirk of the Chapter is the Imperial Fists' pathological need to scrimshaw the bones of their dead when off-duty. The only worrying trait that has attracted scrutiny is the Imperial Fists' over-zealous self-castigation. They often make use of a device called the "Pain Glove," which encases the whole body and stimulates its pain neurons. The Imperial Fists constantly feel the need to punish themselves for the smallest inadequacy, failure or infraction.
Raven Guard N/A The Mucranoid and Betcher's Gland are no longer functional. Raven Guard Astartes often develop extremely pale skin and their hair turns black, regardless of their original complexion or colouration. The acceleration of the gene-seed implantation and replication process instigated in the Raven Guard Legion in the wake of the Istvaan V Drop Site Massacre had implications for the Raven Guard Chapter's genetic inheritance with which they would grapple for millennia. The Chapter has rarely been able to field the full ten companies mandated by the Codex Astartes, and particularly gruelling campaigns have resulted in the Chapter operating at perilously under-strength levels for extended periods or being forced to withdraw for decades at a stretch to rebuild. Without recourse to these ancient archives of genetic material tithed in ages past, the Chapter's Initiates would be without several elements of their genetic inheritance. As it is, replication of existing gene-stock takes far longer amongst the Raven Guard than it does in other Chapters, forcing ever more reliance on the gene-tithe stocks of the Adeptus Mechanicus, a reliance that few Space Marine Chapters would be comfortable with given the differences in outlook between the two Adepta.
Salamanders N/A While it can be said that the Salamanders' gene-seed may not be mutated or deficient, their physical appearance is striking, most likely brought about by a combination of the phentotypic effects created by a biochemical interplay of their gene-seed, the erratic gravitational and radioactive forces on Nocturne, and the unique genetics of the human population that has evolved to survive them. These factors have contributed to the peculiar reaction of the Astartes' Melanochrome gene-seed organ within the Space Marines native to the fiery world, resulting in an individual Battle-Brother's skin becoming obsidian-black and their eyes blazing with a burning red glow. As far as can be ascertained by the Magi Biologis of the Adeptus Mechanicus, the Salamander's gene-seed appears to be both stable and as yet uncorrupted. An unusual trait of the Salamanders is that their Battle-Brothers tend to be slower in reflex reaction than other Chapters, though the origin of this factor is debated and has not been attributed to any factors present in the gene-seed.
Space Wolves N/A The Space Wolves' gene-seed is as unique as it is deadly. The Canis Helix grants a Space Wolves Astartes animalistic abilities such as an enhanced sense of smell as well as enlarged canine teeth and extreme hirsuteness. As Space Wolves Astartes grow older and more experienced in battle, the Canis Helix causes additional physical alterations: their hair turns grey, their fangs grow even longer into veritable tusks, their skin becomes even more leathery, and, in some rare cases, their eyes turn yellow. Aspirants who are likely to fall prey to the Wulfen mutation inherent within the gene-seed of Leman Russ do not do so after immediately imbibing the Canis Helix mixture, but usually over the weeks and months of training that follow afterwards. One of the most important aspects of their trial of initiation is that the Aspirant show himself able to keep this bestial side under control, even while making his way through the Fenrisian wilderness in harsh conditions. Those that fail to do so will transform into Wulfen, transforming into savage, malformed lupine mutants, and remain forever in the wild.

Traitor Legions

Legion Name Summary
Black Legion Before their corruption by Chaos during the Horus Heresy, the gene-seed of this former Space Marine Legion (known as the Sons of Horus and before that, the Luna Wolves) was perfectly pure and unusually potent, since it was derived from the genome of Horus, who was generally considered the greatest of the Primarchs. However, following their corruption by Chaos, the Black Legion's Space Marines started to exhibit random genetic mutations, and it is likely that this taint now affects their gene-seed as it has almost all of the Traitor Legions.
Death Guard The Death Guard's gene-seed always reflected the gaunt, shadow-eyed qualities of their Primarch Mortarion. They were also known to be quite hardy and were able to fight in the harshest and most toxic of environments. After their corruption by the Plague God Nurgle, their outward appearance now reflects the corruption and the rot that riddles their dark souls.
Emperor's Children The Emperor's Children's gene-seed was perhaps the most pure and stable of all the Space Marine Legions before the start of the Horus Heresy. Their ethos for the attainment of perfection was ingrained into their Legion's beliefs and doctrine. Every enhancement produced by the gene-seed functioned at peak efficiency, allowing these Space Marines to achieve their full potential in battle. No other Space Marine Legion achieved such a goal, and the technology and expertise required have never been rediscovered in the millennia following the Horus Heresy. Like all the Traitor Legions, however, the Emperor's Chidlren's gene-seed is now so corrupted and riddled with Chaos mutations that it is functionally useless for creating new Astartes.
Night Lords The gene-seed of the Night Lords seems to be surprisingly pure. In fact, since their corruption, the Night Lords seem to bear the least evidence of Chaos mutation out of all the Traitor Legions. It is not known whether this is due to an unusually stable gene-seed stock, or the fact they rarely associate themselves with a particular Chaos power for any length of time. Although the Night Lords are distinguished by the phenotypical traits of jet black eyes and pale skin, their real legacy may be psychological. They tend to display a tendency for paranoia and self-destructive behaviour.
Thousand Sons This Traitor Legion's gene-seed, drawn from the Primarch Magnus the Red, was always genetically unstable and prone to rapid mutation, leading to the development of psychic powers in the majority of Thousand Sons Astartes but also to a terrible mutational degeneration into the creatures who would later be recognised as Chaos Spawn and which was known at the time as the "Flesh-change." The Blood Ravens Chapter may be the Loyalist descendants of the Thousand Sons, which would explain both their unusual psychic abilities but also their tendency to be easily corrupted by Chaos.
Word Bearers The gene-seed of the Word Bearers was originally thought to be pure, but events subsequent to the Horus Heresy revealed the weaknesses inherent in their genetic make-up. The Space Marines of the Word Bearers have a marked tendency towards dogged, unquestioning belief and stubborness that verges on insanity. Since the Heresy, their gene-seed has become corrupted beyond redemption by exposure to the energies of the Warp and those negative traits have been magnified to hideous proportions. The Word Bearers do not display a particular tendency towards mutation, though those who are gifted with such "blessings" of Chaos are much favoured amongst their Host.

Cursed Founding

The 21st Founding was the largest Founding of Space Marine Chapters since the Second Founding following the Horus Heresy. It took place in the 36th Millennium shortly before the start of the Age of Apostasy. The focus of the 21st Founding for the Adeptus Mechanicus was perfecting and removing the existing, identified deficiencies in flawed Adeptus Astartes gene-seed, and ultimately the production of new and improved Primarch-like Space Marines as part of what was called "Project Homo Sapiens Novus". Unfortunately, the Mechanicus' Genetors proved far less skilled in the genetic sciences than the Emperor of Mankind, and their efforts resulted in the development of seriously flawed gene-seed that was used to craft the organ implants for the new Chapters.

The 21st Founding is also known simply as the "Cursed Founding," because of the appalling bad luck that seems to dog the Chapters that were created by it. Worse still, some of these Chapters have developed unexpected genetic idiosyncrasies, mutations that strain the tolerance of the Inquisition and threaten the Chapter's survival. As a result, the Chapters of this Founding have gradually dwindled in size as their inability to raise and induct new recruits means that their battle casualties cannot be replaced. The most seriously afflicted Chapters exhibited spontaneous and extreme physical corruption, turning them into a race no longer human or sane. Most of the Space Marine Chapters Founded during this time eventually turned Traitor and swore themselves to Chaos or met a gruesome end at the hands of other Space Marine Chapters and the Inquisition's Ordo Hereticus.


  • Codex Adeptus Astartes - Space Marines (8th Edition), pp. 10-11
  • Chapter Approved - Fourth Book of the Astronomican, "The Cursed Founding", by Andy Hoare, Graham McNeill & Phil Kelly, pp. 4-9
  • Codex Imperialis
  • Codex: Space Marines (5th Edition)
  • Codex: Space Marines (4th Edition)
  • Codex: Ultramarines (2nd Edition)
  • Imperial Armour Volume Nine - The Badab War - Part One
  • Imperial Armour Volume Ten - The Badab War - Part Two
  • Index Astartes II, "The Cursed Founding - An investigation into a mysterious Space Marine founding"
  • Warhammer 40,000 Compendium (2nd Edition), "Chapter Approved - Legiones Astartes" by Rick Priestley, pp. 6-10
  • White Dwarf 260 (US), "Index Astartes: The Cursed Founding"
  • White Dwarf 98 (UK), "Chapter Approved" by Rick Priestley
  • Blood Gorgons (Novel) by Henry Zou
  • Salamander (Novel) by Nick Kyme
  • Legion of the Damned (Novel)
  • Space Marine (Novel), by Ian Watson