Mutations and Genetic Evidence
Sometimes the DNA code changes. A single letter is swapped, added, or dropped, and the result can be harmless, harmful, or occasionally helpful. These changes, called mutations, are a major source of variation, and the patterns in DNA also serve as powerful evidence for how living things are related.
This lesson explains what mutations are and how genetic material provides evidence in science.
A mutation is a change in the DNA sequence. Mutations can be caused by mistakes during DNA copying or by outside factors like radiation and chemicals. Most mutations are neutral or harmful, but a few are helpful and provide variation for evolution. Similarities in DNA between species are used as genetic evidence of common ancestry.
What causes a mutation?
A mutation is any change to the DNA sequence. Some happen by accident when a cell copies its DNA, since the process is not perfect. Others are caused by mutagens, outside agents such as ultraviolet light, radiation, or certain chemicals. A mutation in a body cell affects only that individual, but a mutation in a sex cell can be passed to offspring.
Are mutations good or bad?
Most mutations are neutral, meaning they have no noticeable effect. Some are harmful, disrupting a protein and causing disease. A small number are beneficial, giving an individual a trait that helps it survive. Over long periods, those rare helpful mutations, passed to offspring, provide the variation that natural selection acts on. In that sense, mutations are the ultimate source of new traits.
| Mutation effect | Result |
|---|---|
| Neutral | No noticeable change |
| Harmful | Can cause disease or a nonworking protein |
| Beneficial | Provides a helpful new trait |
How is DNA used as evidence?
Because DNA is passed from parents to offspring, it also records relationships. Species that share more of their DNA sequence are more closely related and share a more recent common ancestor. Scientists compare DNA to build family trees of life, to identify individuals in forensics, and to trace how populations have changed. This is why genetic evidence is one of the strongest supports for the theory of evolution.
Watch: A Short Video Lesson
Miss Estruch walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for mutation questions
- Define the change: a mutation alters the DNA sequence.
- Identify the cause: a copying error or a mutagen like radiation.
- Classify the effect: neutral, harmful, or beneficial.
- Note whether it can be inherited (sex cell) or not (body cell).
- For genetic evidence, more shared DNA means a closer relationship.
Practice questions
- What is a mutation?
- Name one thing that can cause a mutation.
- Are most mutations helpful, harmful, or neutral?
- Why are beneficial mutations important for evolution?
- What does it mean if two species share a large amount of DNA?
- True or false: a mutation in a body cell is passed to offspring.
Answers:
- A change in the DNA sequence.
- Any of: a copying error, radiation, ultraviolet light, or certain chemicals.
- Neutral.
- They add helpful new traits that natural selection can favor.
- They are closely related and share a recent common ancestor.
- False. Only mutations in sex cells can be inherited.
Where this fits
Mutations are changes to the DNA, genes, and chromosomes you studied earlier, and they supply the variation behind evolution and natural selection. Genetic evidence also supports the story told by genetic variation, common ancestry, and cladograms. Find all topics on the ASVAB General Science Learning Hub.
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