Genophage

The genophage was a biological weapon deployed against the krogan by the turians during the Krogan Rebellions. Rather than killing the krogan outright, it infected the species with a genetic mutation that collapsed the chance of viable pregnancies, leaving the population in a long, inexorable decline. Engineered by the salarians and unleashed by the turians, the genophage shaped krogan culture, galactic politics, and the conscience of those who had built it for more than a thousand years.

How the genophage worked#

The genophage did not reduce the fertility of krogan females so much as the probability of viable pregnancies. Many krogan died in stillbirth, and most fetuses never reached even that stage, their nervous systems prevented from developing. The mutation infected every cell in each krogan, which blocked any attempt to counteract it through gene therapy. It worked by altering hormone levels, and in theory the damage could be repaired by inducing the affected glands to compensate in their production.

Although it had not been designed as a sterility plague, the combination of rare viable pregnancies with the krogan's general disunity and proclivity for violence left them a dying race bound for extinction. After centuries under its shadow, the certainty of their species' end bred a kind of fatalism that made the krogan especially dangerous, indifferent to whom they attacked or what risks they took. The psychological toll was severe, as the krogan endured the disposal of vast piles of dead children. A few individuals, Urdnot Wrex among them, tried to rebuild the species by focusing on breeding, though the krogan's inherent belligerence usually frustrated such efforts.

Origins and deployment#

The genophage was originally developed by the salarians, who believed its consequences would be so catastrophic that no one would ever actually deploy it, intending instead to wield it as a deterrent. The turians, however, held a very different military philosophy, favoring massive retaliation. Once the weapon was complete, the turians used it at once, and krogan numbers began to dwindle rapidly. Any female krogan capable of carrying young to term became a prize of war, fought over viciously, and a female warlord named Shiagur used her own fertility as a bargaining chip to draw the strongest males into her army.

There was no known cure. Some krogan groups invested in companies such as Binary Helix in the hope of finding one, but these efforts were thwarted by a shortage of krogan scientists and a general disinterest among other species in seeing the krogan population revived. The desperation gave rise to bizarre remedies, including a black-market trade in krogan testicles fueled by the unfounded belief that transplants could counter the genophage's effects.

Saren's cure and the modernized variant#

During the hunt for the rogue Spectre Saren Arterius, it emerged that he had developed a genophage cure, possibly with aid from Binary Helix or even the Reaper Sovereign, and was using it to breed a krogan army on Virmire. The exact nature of that cure was never learned, as it was lost when Commander Shepard and Captain Kirrahe destroyed the facility, an act that could open a rift between the Commander and Wrex if he had joined the team.

The salarian scientist Mordin Solus later explained that the krogan had begun evolving a resistance to the original genophage, raising the rate of viable pregnancies, and that he and his colleagues had engineered a new variant to hold population growth to pre-industrial levels. Mordin came to feel deep guilt over his work, even as he maintained the genophage had been necessary. In the course of helping Mordin track down his former student Maelon, Shepard could choose to destroy or preserve research Maelon had gathered toward a true cure.

The genophage in the Reaper War#

By the time of the Reaper invasion, the question of curing the genophage had become a central point of galactic politics. A salarian special-tasks mission had recovered surviving krogan females and brought them to Sur'Kesh, though in many accounts only one, nicknamed Eve, endured. Cerberus sought to preserve the genophage to prevent an alliance between turians and krogan, while the salarian leadership feared that a revived krogan population would one day seek revenge for the weapon's use.

If the necessary research had been preserved, a cure could be completed and dispersed across Tuchanka through the Shroud facility, though the salarian dalatrass revealed that her people had secretly sabotaged the Shroud and offered support in exchange for hiding the truth. Depending on Shepard's decisions and on who had survived earlier events, the cure could be released in full, ending the genophage and bringing the krogan into the alliance against the Reapers, or it could be quietly thwarted. In some accounts Mordin overrode the sabotage and sacrificed himself to disperse the cure; in others the cure failed or was deliberately faked, and if Shepard ultimately chose to merge organic and synthetic life through the Crucible, the genophage was cured regardless of what had happened on Tuchanka.

Records uncovered later in the Citadel Archives, dated to the deployment in 710 CE, depicted turian officers and a lone salarian at the Shroud in the moments before activation. The salarian protested that his government had never authorized the release and called the act genocide, only to be restrained as the lead turian declared that the salarians would one day be grateful, then triggered the genophage.