Gene mutations
| English | Chinese | Pinyin |
|---|---|---|
| mutation | 突变 | tū biàn |
| base sequence | 碱基序列 | jiǎn jī xù liè |
| substitution | 替换 | tì huàn |
| deletion | 缺失 | quē shī |
| insertion | 插入 | chā rù |
| frameshift | 移码 | yí mǎ |
| reading frame | 阅读框 | yuè dú kuāng |
| silent mutation | 沉默突变 | chén mò tū biàn |
| natural selection | 自然选择 | zì rán xuǎn zé |
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:
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:
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.
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?
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.
Every triplet after the change is read wrongly, so the protein is usually badly affected.
Match each mutation to its effect.
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