Mutation
A mutation is a sudden, heritable change in genetic material that may alter a nucleotide sequence, gene function, chromosome structure, or chromosome number.
In one line: Point mutation changes a point; frameshift shifts the reading frame; chromosomal mutation changes a larger chromosome segment.
Concept Practice Coming SoonUnderstand it
- Mutations create new genetic variation by changing DNA or chromosomes.
- A point mutation affects a single base pair and may change a codon.
- A frameshift mutation occurs when insertion or deletion of bases shifts the reading frame, often changing many amino acids downstream.
- Chromosomal aberrations involve larger structural changes such as deletion, duplication, inversion, or translocation.
- Some mutations are harmful, some are neutral, and a few may be useful in a particular environment.
- In inheritance questions, mutation is important because it can create new alleles and may cause genetic disorders if it affects germ cells or key functional genes.
Example
Rule to remember
Point mutation changes one base pair.
Frameshift mutation results from insertion or deletion not in multiples of three.
Chromosomal aberrations include deletion, duplication, inversion, and translocation.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1If a DNA sequence has one base substituted and only one codon changes, classify it as a point mutation.
- 2If one base is inserted and all later codons are regrouped, classify it as a frameshift mutation.
Method you can reuse
- 1Identify whether the change is in a nucleotide sequence or chromosome structure.
- 2Check if one base pair is substituted.
- 3Check whether insertion or deletion changes the reading frame.
- 4For chromosome-level changes, name deletion, duplication, inversion, or translocation.
Visual tip
A sequence diagram can show normal codons compared with altered codons after substitution, insertion, or deletion. For chromosomal aberrations, label lost, repeated, reversed, or transferred segments.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why can an insertion or deletion cause a frameshift mutation?
Think first, then show answerHide answer
Common wrong answer
Calling inversion a point mutation is incorrect; inversion is a chromosomal structural rearrangement involving a segment.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
Answer plan
- 1
Enough for 1 mark
A mutation is a sudden, heritable change in genetic material that may alter a nucleotide sequence, gene function, chromosome structure, or chromosome number.
- 2
Add for 2 marks
Example: Sickle-cell anaemia is linked to a point mutation in the beta-globin gene, where a change in one codon alters the amino acid sequence of haemoglobin.
- 3
Add for 3 marks
Mutations create new genetic variation by changing DNA or chromosomes.
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