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Evolution is made possible by the variation that builds up in genomes due to generations of errors, interference, and alteration of DNA. This episode, we explore the science and study of Mutations.
In the news
A Neanderthal multi-tool made from cave lion bone
A terror bird bone with crocodilian tooth marks
A dinosaur dance floor in Colorado
Triassic reptiles with feather-like integument
The Key to Our Evolution
The DNA within our cells is constantly replicating itself as cells grow and split and give rise to new cells. A mutation, put simply, is a change in the genetic sequence during this process.
A mutation can be the loss, gain, or replacement of a single nucleotide (A, C, G, or T) or it can be a larger change that affects an entire chromosome. Some mutations are caused simply by errors in DNA replication, while others are caused by external forces – like chemicals or radiation – that interfere with DNA structure.
Despite their dramatic reputation, most mutations have little to no effect on an organism. Many of these errors are corrected by various DNA repair mechanisms within a cell, and even if a mutation isn’t fixed, a tiny change is harmless in most parts of the genetic code. Besides that, a cell that experiences a dangerous mutation is more likely to simply die off than have an adverse effect on the rest of the body. All of this means that mutations rarely contribute any significant change – positive or negative – to an organism.
What mutations do contribute is variation. Every cell experiences many mutations, and this means that every new cell in a body and every offspring of a parent has a slightly different genetic code than what came before. Some of these differences might manifest as a change in size, color, or functioning, while most will simply be an unnoticeable typo in the genome. Thanks to this variation, every organism is different, and those differences can determine an organism’s susceptibility to disease, ability to digest food, likelihood of experiencing more mutations down the line, and countless other little effects. And when one of these changes persists through the generations, whether by chance or because it somehow improves an organism’s odds of survival, species evolve.
Arguably, every gene in our bodies is a mutation, since they’ve all changed in some way from our distant ancestors. Scientists study the role of mutations in evolution by comparing DNA across living species. In some cases, a single mutation can be identified as the first step that allowed for significant changes down the line, such as in the evolution of snake venom or the spread of lactose tolerance across humans.
The constantly mutating nature of life also allows for a technique called a molecular clock: by comparing the genetic differences between two living lineages and estimating the rate that mutations have accumulated, scientists can estimate how long ago those lineages split. By itself, a molecular clock estimate is only so useful, but when combined with fossil evidence, these genetic records of change can help us place confident dates on significant events in evolutionary history.
Image from Zephyris, CC BY-SA 3.0
Learn More
Genomes – Mutation, Repair and Recombination
Mutations Are the Raw Materials of Evolution
DNA Replication and Causes of Mutation
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