Gene mutations
Introduced| English | Meaning |
|---|---|
| mutation/mjuːˈteɪʃn/ | A change in genetic material, such as a DNA sequence or chromosome structure. |
| base sequence/beɪs ˈsiːkwəns/ | The order of nucleotide bases along a strand of DNA or RNA. |
| substitution/ˌsʌbstɪˈtjuːʃn/ | A mutation in which one nucleotide or base pair is replaced by another. |
| deletion/dɪˈliːʃn/ | A mutation in which one or more nucleotides are lost from a DNA sequence. |
| insertion/ɪnˈsɜːʃn/ | A mutation in which one or more nucleotides are added to a DNA sequence. |
| frameshift/ˈfreɪmʃɪft/ | A change in how codons are grouped after insertion or deletion of a nucleotide number that is not a multiple of three in a coding sequence. |
| reading frame/ˈriːdɪŋ freɪm/ | reading frame |
| silent mutation/ˈsaɪlənt mjuːˈteɪʃn/ | silent mutation |
| natural selection/ˈnætʃərəl sɪˈlekʃn/ | The process in which inherited traits that improve survival and reproduction become more common in a population over generations. |
When the code goes wrong
- A gene mutation 突变 is a change in the base sequence 碱基序列 of DNA.
- A change in the code can change the polypeptide that is made.
- How much it changes depends on the type of mutation.
Mutation type lab
Compare substitution, insertion and deletion using their effect on the code.
A gene mutation is:
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A gene mutation is a change to the sequence of bases in a DNA molecule.
Substitution 替换
- A substitution swaps one base for a different base.
- It changes at most one amino acid — and sometimes none at all, because the code is degenerate (the new triplet may still code for the same amino acid).
Substitution, deletion 缺失 and insertion 插入 mutations
A substitution mutation changes:
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Only one triplet is altered, so at most one amino acid changes — and the degenerate code means sometimes none does.
A substitution can sometimes leave the amino acid unchanged.
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Because the code is degenerate, the new triplet may still code for the same amino acid — no change.
Deletion and insertion: frameshift 移码
- A deletion removes a base; an insertion adds an extra base.
- Either one shifts the reading frame 阅读框 — every later triplet is read wrongly.
- So these usually change many amino acids after that point, with a large effect.
original: CAT-GGA-TCC-ATG
substitution: CAT-GCA-TCC-ATG one codon changed
deletion: CAT-GAT-CCA-TG? frame shifts → all later codons change
Why do deletions and insertions usually have a large effect?
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Adding or removing a base shifts the reading frame, changing all the triplets that follow (a frameshift).
Adding or removing a base shifts the reading frame — this is called a ______ mutation.
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Every triplet after the change is read wrongly, so the protein is usually badly affected.
Match each mutation to its effect.
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Substitutions affect at most one amino acid; insertions and deletions cause a frameshift; a silent mutation changes nothing.
Not every mutation matters
- The genetic code is degenerate, so some base changes still code for the same amino acid — a silent mutation 沉默突变.
- Most mutations are harmful or neutral, but a rare beneficial one is the raw material for natural selection 自然选择.
You've got it
- a mutation = a change in the DNA base sequence
- substitution: one base swapped → changes ≤ 1 amino acid (sometimes none — degenerate code)
- deletion / insertion: shift the reading frame → change many later amino acids (frameshift)
- frameshift mutations usually have a much larger effect than a substitution