|Homeworld||Newfound, near Ultramar|
|Specialty||Copying the Ultramarines|
|Allegiance||Imperium of Man|
|Colours||Red & White|
- "Oh but we CAN be Ultramarines!" - No-name Genesis Chapter Master
The Genesis Chapter is generally held to be the closest of the Ultramarines’ Successors, both doctrinally and astrographically. The Chapter holds to the wisdom of the Codex Astartes in every possible way. The Chapter’s home world of Newfound is a neighbour of the Ultramarines’ Realm of Ultramar, and its brothers commonly undertake at least one pilgrimage to the Shrine of the Primarch whilst popping over for tea and sugar.
The Chaplains of the Genesis Chapter regard the Codex Astartes as utterly sacrosanct, and they go to great lengths to ensure the Chapter’s adherence to its tenets. Any points of contention are debated thoroughly, with recourse to the opinions of the Ultramarines’ Chaplains for final ratification in order to ensure there is no doctrinal drift between Progenitor and Primogenitor whatsoever. So in essence whatever the Spiritual Liege orders; the Genesis Chapter will follow blindly, since if they cannot decide an action, they'll check with the Ultramarines to make a decision.
Because the Genesis Chapter maintains such close links with its Progenitor, the two Chapters frequently cruise through the stars together, looking for battles/hos/Codex deviants to bully. Genesis Chapter squads routinely fill gaps in Ultramarines’ companies should they fall below codex strength due to battle losses or other commitments. Individual Genesis Chapter Battle-Brothers have even been seconded to the Ultramarines to temporarily fill empty specialist positions in the Ultramarines Chapter such as Librarius and Forge staff. and what do they get in return? FUCK ALL that's what.
If proof were ever needed to show that the Ultramarines were in breach of their own limitations on chapter size set down in the Codex Astartes, the Genesis chapter would be it as they are essentially an entire spare chapter for the Ultramarines to use as private reserves and can ensure (unlike some other chapters) that they never have to undergo a long painful period of rebuilding after a brutal campaign, and thus retain their Mary Sue status.
The Genesis Chapter itself, however, did get out played by some Night Lords during the early parts of the 13th Black Crusade. Seeking to stop the Night Lords from landing on a planet, a cruiser launched its drop pods while still in orbit, looking to use them as makeshift boaring torpedos and storm the bridge. However, the Night Lords instead had laid a trap and decided to blow up half of the orbiting moon to take out the cruiser after killing the marines who had boarded their own Strike Cruiser. inside. To be fair, they did give a pretty good account of themselves. They only possessed a few squads led by a veteran sergeant and they managed to take half of the Night Lords with them. Not to mention said veteran sergeant took on the entirety of First Claw and killed Xarl, one of its most fearsome members.
TL;DR: Ultramarines reserve team.
In the Deathwatch there is a hallowed tome referred to as Tulius Insight. To which battle brothers from stricter chapters are directed to if they are having difficulty adjusting from Codex Astartes doctrines to the much looser freedoms allowed by the Ordos Xenos. This tome details how the Codex Astartes can still be applied to the marine's duties, even when away from their parent chapter in situations where it might not be apparently clear.