Genetic Mutation
Explain mutation as a change in DNA sequence that arises without regard to an organism's needs, name causes such as copying errors, radiation and some chemicals, and distinguish neutral, harmful and beneficial effects
What a learner can do afterwards
- Defines mutation as a change to DNA sequence that does not arise because an organism needs it
- Names copying errors and examples of mutagens, such as UV radiation and some chemicals
- Explains that mutations create new gene versions, while mixing existing versions creates new combinations
- Explains how an inherited beneficial mutation can become more common through natural selection
1 · Read
Genes are sections of DNA. A mutation is a lasting change in DNA's letter sequence. Letters can be replaced, added or removed. Mutations do not arise because an organism needs them. Here, random means that a change happens without regard to whether it will help.
DNA copying errors can become mutations if they are not corrected. Mutagens increase the chance of mutations. Examples include UV radiation from sunlight and some chemicals in tobacco smoke. Cells can repair DNA damage, so damage does not always leave a mutation.
Mutations can be neutral, harmful or beneficial for survival or reproduction. Many have no effect on either, so they are neutral. In an imagined forest, a darker-shell mutation helps beetles hide from birds. Where colour makes no difference to survival or reproduction, it is neutral.
Mutation creates new gene versions. Mixing existing versions creates new combinations without a new mutation. Natural selection can make an inherited version more common if its carriers leave more surviving offspring. Spread is not guaranteed. In humans, mutations in eggs or sperm can be passed to children; a mutation only in skin cells is not normally inherited.
Mutations change DNA without regard to an organism's needs. They can be neutral, harmful or beneficial. Natural selection may make an inherited helpful version more common.
Lesson and questions written for this dataset. OpenStax and Khan Academy records were studied for scientific background.
Readings written for this dataset. Video links credit Khan Academy.
More to read
A DNA change and its effect
Finding a mutation tells you that DNA's sequence has changed. It does not tell you the effect without further evidence.
A gene change may alter a protein and affect how it works. Other changes leave a protein doing the same job. A mutation is neutral if it has no effect on survival or reproduction. Harmful mutations reduce survival or reproduction; beneficial ones improve them.
The environment matters. A colour change may help an animal hide from predators in one habitat but offer no advantage elsewhere. The mutation did not arise because the animal needed camouflage. Natural selection can later make an inherited version more common if its carriers leave more surviving offspring.
Comparing DNA before and after
Compare two records of the same short DNA section: before, A G C T; after, A G T T. Both contain four letters. At the third position, C has been replaced by T. This is a substitution.
An insertion adds one or more letters. A deletion removes one or more letters. These describe how the sequence changes, not whether the change helps or harms the organism.
Mutations create new gene versions. Mixing versions that already exist can create new combinations without creating a new version. If no new mutation occurred for a time, existing genetic differences would not all disappear. Natural selection could still act on inherited differences already present.
Repair, lasting changes and inheritance
Cells can repair DNA damage and correct copying errors. If repair restores the original sequence, that site has no lasting mutation. A copying error that remains uncorrected can leave a changed sequence.
A neutral mutation is different from a repaired error. Neutrality describes the effect of a change that remains: it does not affect survival or reproduction.
In humans, a mutation carried in an egg or sperm can enter an offspring's DNA. A mutation found only in skin cells is not normally inherited by children, although it can be copied when those skin cells divide.
UV radiation can damage skin-cell DNA and raise skin-cancer risk. Repair reduces damage, but does not remove every risk.
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