Fine-tuning human genetic-level transformation

Question

Suppose humans discovered a beautiful new world they wanted to inhabit, far from the political machinations and military affairs of the alien-populated universe. They established a few colonies on the planet's surface, with differing levels of technology.

One of the native fauna serves as an agent of change: it is similar to a mosquito, but each bite slightly alters the genetic structures of its victim. This allows flora and fauna alike to adapt to their environment. Humans, for example, cannot eat the local food until a few days of exposure to the mosquitoes alters their body enough to make the food compatible.

This change needs to be slow enough to

1. keep the victim alive and
2. prevent the changes from being quickly noticed,

but fast enough to

3. be obvious enough to distinguish someone living on the planet for years from someone who just arrived.

My current idea is for the mosquito bites to modify 1% of the subject's unaltered genetic structure each year. Over time, these changes manifest as unusual hair or eye color, hardening of the skin, and similar predominantly cosmetic changes. Across generations, these changes are much more profound, such as introducing new organs or appendages.

My Questions

1. Is this a reasonable rate of change to achieve my three objectives?
2. How can I calculate the amount of genetic change a given individual has experienced for a given number of years of exposure?
3. How can I calculate the amount of genetic change between generations?

Answer 1

You're effectively describing a virus - an organism which injects its own DNA into an existing cell, and re-purposes it.

And the answer is that the sort of slow change you're looking for is not going to work.

Why? Because iffy things happen when cells starts displaying characteristics which your immune system can't recognize. It's why people who've had organs replaced have to take immunosuppressants.

And so, the infected cells would be attacked by your body. You'd run a fever, and maybe start manifesting worse symptoms as your immune system went on the offensive and failed to deal with the infection.

The only way for an organism (human, in this case) which is already born and alive to survive a change to its DNA (assuming that the change itself does not result in some terrible disease, etc.) is for that change to be implemented throughout the entire organism in one quick go.

The event would have to be very, very fast and aggressive. The subject may even suffer clinical death in the process, but be revived by medical teams, or the virus itself by some clever mechanism. Keep in mind that this is science fiction, and that a doctor would most likely say you'd simply die.

Answer 2

Look at it from the opposite point of view. We and chimps and bonobos share 99% of our DNA. Have you ever heard of a virus which has changed a person into something resembling a chimp? That would be a 1% change.

How long would that change take? I'd guess at least a couple of dozen to a couple of thousand generations. 1% a year? No way. Changes on that time scale would have to be orders of magnitude smaller.

Consider that the human body "turns over" about every 7 years (crudely speaking). So, each "stage" of change should be about that long. And if it takes, say 10 changes to develop the entire new enzyme/metabolic pathway to digest a new food, then that's 70 years or 3-4 generations (and much less than a 1% change of the human genome).

Consider some of us have the ability to digest lactose. Read up on how long that has taken. I grant you that "intelligently designed" changes could speed up the process considerably, but changing too much at once (in a single organism) just isn't survivable. That's why death is part of life.