Definition
Endogeny
Endogeny refers to the condition of having an internal cause or origin. In genetics, it describes the process by which an external genetic element—such as a virus—becomes a permanent, heritable part of an organism’s own genome.
Endogenisation of Viruses
The human genome is characterised by a high proportion of “junk DNA” that is actually viral in origin. This occurs through a specific symbiotic trajectory:
- Infection: A retrovirus infects a host cell and uses reverse transcriptase to integrate its code into the host’s DNA.
- Germ Line Invasion: If the infection occurs in an egg or sperm cell, the viral code can be passed down to future generations.
- Endogenisation: Over evolutionary time, the viral code becomes “endogenous.” While it may initially cause disease, it often evolves to be neutral or even beneficial to the host.
Observation
At least eight per cent of the human genome consists of endogenised retroviruses (ERVs). These remnants are evidence of past major evolutionary transitions where pathogens were absorbed and repurposed for critical functions, such as the development of the placenta and the immune system.
Horizontal Gene Transfer
Endogeny is a primary mechanism for symbiogenesis, allowing the “tree of life” to entangle with itself. Through the endogenisation of transposable elements and viruses, complex genetic functionality can be “horizontally” transferred between species and integrated into the host’s hereditary line.