Selection in a test tube

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Selection in a test tube

In the RNA world, RNA evolved to perform all sorts of different jobs — and that is exactly what Andy's lab is trying to do now: evolve RNA molecules that perform useful jobs, such as binding to a tumor cell or stopping viral replication. This technique is called directed evolution.

How do biologists "evolve" RNA in a test tube? The same way that a population of organisms evolves in the real world: natural selection. It works like this:

Natural selection
in the wild Artificial selection
in the lab

green and brown beetles on a tree various RNA molecules

1. There is variation in a population of organisms. 1. There is variation in a population of RNA molecules.

birds eat more green beetles than brown Some RNA molecules perform jobs that make them more likely to survive than others

2. Some variants are more likely to survive than others. 2. RNAs that perform a particular job are more likely to be selected than others. Selected RNAs are removed from the original pool.

beetles reproduce RNA molecules replicate

3. Survivors reproduce. 3. Selected RNAs are copied.

now the beetle population has a greater proportion of brown beetles now the RNA population has a greater proportion of useful molecules

4. The population has evolved and now contains more individuals with the selected trait. 4. The population of RNA has evolved and now contains more useful molecules.

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As time passes, selection and reproduction (steps 2-4) are repeated for each generation.

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After many rounds of selection, all of the beetles are brown

5. After many rounds of selection, the entire population has the selected trait. 5. After many rounds of selection, the entire population consists of useful molecules.

So natural selection can operate on any varying set of individuals that reproduces via genetic inheritance — even if an "individual" is simply a molecule like RNA and is not technically alive (whatever "alive" is)!

The RNA world


	Dig deeper: Find out how Andy uses mutation to his advantage or learn more about the process of natural selection.

Undirected evolution

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