Genetic Metamorphosis

Means by with the Tarchannens, a non-sentient humanoid race, reproduce. They implant a reproductive DNA strand, similar to a parasite, into an alien host's thymus.

Onset of symptoms can vary from days to an hour; blood chemistry changes, the skin develops blotchy surface veins and radiates its own light, and two of the middle fingers fuse. The immune system is attacked, causing a drop in blood pressure and body temperature. The host's DNA is altered and they change into an alien lifeform.

The process can be reverse if the parasite is removed.