Perhaps most surprisingly, retroviruses have played a massive role in human evolution. When a retrovirus infects a sperm or egg cell, its genetic material can be passed down to future generations. Over millions of years, these "fossil" viruses have accumulated in the human genome and are known as . Scientists estimate that 8% to 9% of the human genome is composed of these ancient viral remnants. While most are now inactive mutations, some have been repurposed by our bodies to help regulate the immune system or even aid in the development of the placenta during pregnancy. Conclusion
The hallmark of a retrovirus is its ability to integrate its own genetic material permanently into the host's genome. This process occurs in several distinct stages: Retrovirus
: The enzyme reverse transcriptase "back-transcribes" the viral RNA into a double-stranded DNA copy. Scientists estimate that 8% to 9% of the
Retroviruses are responsible for several significant human diseases. The most well-known is , which attacks the immune system's T-cells and can lead to AIDS . Other notable human retroviruses include: This process occurs in several distinct stages: :