Clan Weyrloc is a large tribe of krogan on Tuchanka. It is tied to the Blood Pack due to the Blood Pack founder being a chief of the clan. In 2185, the clan was based in a hospital awaiting results from a project to cure the genophage. Clan Weyrloc planned on expanding their numbers to overcome Clan Urdnot, before launching a war against the rest of the galaxy. Commander Shepard's team will need to fight through the clan members as they make their way to rescue Maelon, Mordin's student, even killing Chief Weyrloc Guld in the process. But in truth, Maelon was willingly helping Weyrloc cure the genophage, believing that the clan was willing to do what was necessary to cure it, even if it meant experimenting on humans and their own kinsmen.
Despite the death of Weyrloc Guld and most of his lieutenants, along with the further losses to Clan Urdnot afterwards, the clan turns out to have ultimately survived, albeit reduced to a mere shadow of its former glory. Assuming he was not killed by Mordin in the previous game, the remaining clan members blame Maelon for their downfall and put a bounty out on his head, forcing him into hiding. After the genophage is cured, Maelon will message Shepard and express his hope that now that Clan Weyrloc have the cure they wanted, they'll leave him alone.