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Gene-seed is the unique genetic material used to transform a normal human into a super-human Space Marine.


A table showing the calculated chances of gene-seed mutation in the First Founding Chapters.

It is used to grow the artificial organs that distinguish an Adeptus Astartes from an ordinary human, and helps alter the human's biology to accept the implanted organs. Gene-seed is a Space Marine Chapter's most precious resource, and is conserved by extracting the progenoid glands from fallen Battle-Brothers for return to the Chapter's fortress-monastery.[Needs Citation]

Several Chapters have unique gene-seed flaws that cause differences in their Marines' physiology and behavior. These differences can be merely cosmetic (for instance, all Death Spectres are albinos), while others can have drastic effects that are either a blessing or a curse (or both) for their Chapters, such as the Blood Angels or the Space Wolves.[Needs Citation]

Some Chapters' gene-seed are inherently more stable than others, and variations in certain Chapters' methods of implantation have resulted in further degradation in some cases. The gene-seed of the Ultramarines is considered the most stable and thus they are the most preferred source of gene-seed for creating new Space Marine Chapters.[Needs Citation]



Even before the Emperor had unified Terra, His armies included genetically altered warriors, the Custodes and the Thunder Warriors. Although these soldiers were more powerful than the later Space Marines, they were fewer in number and had a shorter lifespan. It was during this period that the techniques for restructuring genetic codes were perfected. Individual germ-cells, called gene-seeds, were isolated and genetically modified, eventually being used to create specific organs that could be implanted into a warrior.[1a] The Emperor was aided by his Terran geneticist cadres, known as the Biotechnical Division.[12]

The development of these organs took many centuries and the research was in fact an off-shoot of the aborted Primarch project. The Primarchs were god-like beings whose powers far outstripped even that of a "regular" Space Marine. Samples of genetic tissue were taken from each of the fetal Primarchs and used to create the gene-seed of the original twenty Space Marine Legions. Thus each of the original Legions (and therefore their Successor Chapters) inherited some traits associated with their specific Primarch.[1a]

While the original gene-seed was created by the Emperor and His scientists, it was only mass-produced after the conquest of the advanced genetic cults of Luna.[8]


The events of the Horus Heresy revealed weaknesses in some Legions' gene-seed. In some cases these defects had been heightened by the accelerated cultivation techniques used to keep the Legions at full strength. After the Heresy and the break-up of the original Legions, genetic banks were established on Terra to produce and store Space Marine gene-seed. These banks were to provide all genetic material for new Space Marine Chapters. To prevent cross-contamination of these genetic stocks, the gene-seed of each individual Legion was isolated, so all new Space Marines would receive gene-seed solely from one specific source. The gene-seed of the Traitor Legions was placed under a time-locked stasis seal (rather than being destroyed as many at the time assumed had happened).[1b]

Subsequent Foundings

After the Heresy, the Space Marine Legions were divided into smaller Chapters. The genetic materials of some Chapters were considered more pure than others and thus, at the time of the 41st Millennium, over half of the thousand known Chapters are descended from the Ultramarines' genetic stock, either directly or through one of their Second Founding Chapters.[1c]

A Marine's gene-seed may be rendered useless by exposure to high levels of radiation. Also, over time a Chapter's gene-seed may change through genetic mutations, so that specific implants become corrupted, producing new effects in Marines, or becoming useless altogether. A corruption in the Chapter's genetic material can lead to the Chapter's extinction. This is why gene-seed must be constantly monitored for mutations.[Needs Citation] Each chapter is obliged to tithe 5% of its gene-seed to the Adeptus Mechanicus on Mars. The first purpose for this is that it enables the Adeptus Mechanicus to monitor the health of each Marine Chapter. The second is that it creates a store of preserved gene-seed to be used for funding new Chapters.[15]

The creation of the gene-seed to be used for founding a new Chapter is a lengthy process. A single suitable gene-seed is selected and used to create a zygote. Zygotes are then grown in culture and implanted into test-slaves, which must be biologically compatible and free from mutation. Test-slaves are little more than physical mediums for the creation of gene-seed, and as such are bound in experimental capsules, where they remain conscious but are completely immobile. The process begins with a single implanted slave, whose body produces two progenoids. These are implanted within two more slaves, that then produce four progenoids; this process is repeated until 1,000 healthy sets of organs are produced, which takes about 55 years of constant reproduction.[15]

Per Imperial law, only the Emperor is authorized to decree the founding of a new chapter. In practice, this is done by the High Lords of Terra speaking in his name.[15]

The Grey Knights are unusual in that the source of their gene-seed is the Emperor's own, unaltered, genetic code.[13][14]

The Twenty First Founding (also known as the Cursed Founding) is notable in that its focus was in perfecting and removing deficiencies in flawed gene-seed. Unfortunately, many of the Chapters created at this time have developed genetic idiosyncrasies, mutations that strain the tolerance of the Inquisition and threaten these Chapters' survival.[2]

The Ultima Founding in M42 saw tens of thousands of new Primaris Space Marines produced thanks to the efforts of Belisarius Cawl, all with the same gene-seed of the Primarchs. Thanks to Cawl's Sangprimus Portum, the gene-seed of the Primaris Marines is closer to that of the original Primarch's than standard versions. This and the three additional implants given to Primaris Marines have made them more genetically stable, enabling gene-seed production at rates not seen since the time of the Emperor.[10]

Implantation and Reproduction

The gene-seed of a Chapter is a precious resource, so it is only given to the most worthy of candidates. Each Chapter has its own traditions and procedures for the selection of recruits, but all are subjected to rigorous testing and genetic screening before the process begins.[3a]

During the later stages of the implantation process, a recruit will often serve as a Space Marine Scout.[3b]

Reproduction of gene-seed is possible through the Progenoid glands, implants whose sole purpose is the replication of gene-seed. A mature gland can be removed by an Apothecary and new organs artificially cultured from it. This is the only source for new implants, so a Chapter depends on its Marines to create other Marines. In the battle-mysticism of the Astartes, the gene-seed is regarded spiritually - although a fallen Marine's body is dead, he lives on as gene-seed that returns to the Chapter.[Needs Citation]

Apothecaries remove Progenoids after they have matured or if a Marine has died in combat.[Needs Citation]


There are nineteen implanted organs - some of which only work properly (or at all) in the presence of other implants. Therefore the removal, mutation or failure of one organ can affect the precise functioning of the others. Because of this, and the fact that each Chapter's gene-seed belongs to that Chapter alone, different Chapters display different characteristics and use different sets of implants and methods of implantation. Throughout the implantation process the Marine must undergo various forms of conditioning in order for the implanted organs to develop and become part of his physiology.[4]

Chapters with known gene-seed flaws

Chaos Space Marines

The renegade Legions and Chapters maintain the process of gene-seed implantation and harvesting, allowing new recruits to be turned into Marines. The specifics of the renegade Marines' methods are unclear, but it is known that Fabius Bile provides recruits for some traitors in return for slaves and other resources.[Needs Citation]

Nearly all of the Traitor Legions' gene-seed suffers from some kind of instability, though it is debated in the Imperium whether this is caused by some inherent "rot" that was present before the Horus Heresy, or simply the result of constant exposure to the warp inside the Eye of Terror. Whatever the cause, this instability hampers the Chaos Space Marines' ability to create new Marines.[Needs Citation]

For this reason, the Traitor Legions will sometimes raid the strongholds of Imperial Chapters to steal stable gene-seed, which is a prized resource within the Eye.[7]

Primaris Marines

The new breed of Space Marines, the Primaris, have a greater level of genetic stability than those of their standard cousins. As a result they have avoided many of the severe defects and flaws of Chapters such as the Blood Angels and Space Wolves while retaining their quirks and unique benefits. The Primaris Blood Angels in particular still possess the Red Thirst, but show no signs of the Black Rage.[11] The chance of genetic deviancy for Primaris Marines is a mere 0.001%.[9] In addition they are physically larger and stronger thanks to the Sangprimus Portum, which gives them genetic material more potent than standard Gene-Seed descended from the Primarchs.[10]