Question 1

Why is 8% of human DNA viral?

Accepted Answer

About 8 percent of the human genome comes from ancient retroviruses that infected our ancestors' egg or sperm cells millions of years ago. Once inside the germ line, the viral DNA became heritable and was passed down through every generation, leaving roughly 100,000 viral fragments scattered across our chromosomes.

Question 2

What is an endogenous retrovirus?

Accepted Answer

An endogenous retrovirus, or ERV, is a retrovirus that long ago inserted its DNA into a host's reproductive cells, making it a permanent, inherited part of the genome. Most ERVs are now broken and silent, but a few remain active or have been repurposed by the body.

Question 3

Did a virus help create the human placenta?

Accepted Answer

Yes. A protein called syncytin, which fuses cells into the barrier of the placenta, originally came from a retroviral envelope gene captured by our ancestors more than 25 million years ago. Every placental mammal carries a similar domesticated viral gene essential to live birth.

dna

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The Ghosts in Your Genome