Explain how mutations change the DNA sequence and can alter proteins and traits, and describe their effects (North Carolina Standard Course of Study, Biology, LS.Bio.6).

What this topic is asking

North Carolina LS.Bio.6 asks how mutations change the DNA sequence and can alter proteins and traits. For the Biology EOC you need the three types of point mutation (substitution, insertion, deletion), why insertions and deletions cause a frameshift, the three possible effects (harmful, beneficial, neutral), and the big-picture role of mutations as the only source of new alleles for evolution. Items often link a base change to a changed protein.

What a mutation is

Mutations happen during DNA replication (copying errors) or because of mutagens such as radiation and certain chemicals. Most are small changes to single bases, called point mutations, but they matter because the order of bases is the code, so changing it can change the message.

The three types of point mutation

To see the frameshift, imagine reading the code three letters at a time: THE CAT ATE. Delete one letter and re-group: HEC ATA TE, and every "word" after the deletion is different. A substitution would change only one letter in one word.

The effects of mutations

A mutation's effect depends on how it changes the protein, and there are three possibilities:

• Harmful. The protein works less well or not at all, which can cause a genetic disorder.
• Beneficial. The protein gives a new advantage, such as resistance to a drug or a useful trait.
• Neutral. There is no noticeable effect, for example a change that does not alter the amino acid or affects a part that does not matter.

Crucially, whether a mutation is harmful or beneficial can depend on the environment: a trait that is a disadvantage in one setting can be an advantage in another. Note also that only mutations in gametes (sex cells) are passed to offspring; a mutation in a body cell affects that individual but is not inherited.

Why mutations matter for evolution

This is the deep reason mutations matter: they are the raw material of evolution. Natural selection can only act on variation that already exists, and the ultimate source of all new variation is mutation. Without mutation, there would be no new alleles for selection to favor or remove, and populations could not adapt to changing environments over time. This links the topic directly to natural selection.

Try this

Q1. Name the three types of point mutation and state which cause a frameshift. [2]

• Cue. Substitution, insertion, and deletion; insertion and deletion cause a frameshift.

Q2. Explain why mutations are essential to evolution. [2]

• Cue. They are the only source of genuinely new alleles, providing the new variation that natural selection acts on.