Mutation and Gene Technology
IB Biology SLΒ· 6 min read
1. Types of Mutationβ β ββββ± 15 min
Mutation
A permanent change in the nucleotide sequence of DNA, arising spontaneously during replication or induced by mutagens (e.g. radiation, chemicals)
Example:
A base substitution in the hemoglobin gene causes sickle cell anemia
Mutations are categorized by their scale: gene mutations affect a single gene, while chromosome mutations affect large segments or whole chromosomes. Gene mutations include base substitution, insertion, and deletion. Insertions and deletions often cause frameshifts that alter all downstream amino acids.
Base substitution: One nucleotide is replaced by another, resulting in silent, missense, or nonsense mutations
Insertion: One or more extra nucleotides are added to the sequence
Deletion: One or more nucleotides are removed from the sequence
Frameshift: Insertions/deletions shift the reading frame, almost always producing non-functional proteins
Explain why a base deletion is more likely to produce a non-functional protein than a base substitution
- 1
The genetic code is read in groups of 3 nucleotides (codons), so the reading frame is critical for producing the correct amino acid sequence
- 2
A base substitution only changes one codon. It may be silent (due to code degeneracy), change only one amino acid, or rarely create a stop codon
- 3
A base deletion removes one nucleotide, shifting the entire reading frame of all codons downstream of the deletion
- 4
All amino acids after the deletion are altered, almost always producing a completely non-functional protein
2. Polymerase Chain Reaction (PCR)β β ββββ± 20 min
Polymerase Chain Reaction (PCR)
A laboratory technique used to amplify (make millions of copies of) a specific target DNA sequence from a tiny initial sample
PCR is used in forensics, paternity testing, and medical diagnostics (e.g. viral testing). The process relies on repeated temperature cycles and requires a heat-stable DNA polymerase called Taq polymerase, isolated from thermophilic bacteria that live in hot springs.
Outline the three main steps of one PCR cycle and what occurs at each
- 1
- Denaturation (~95Β°C): High temperature breaks hydrogen bonds between DNA strands, separating double-stranded DNA into single strands
- 2
- Annealing (~50-60Β°C): The mixture cools, allowing DNA primers to bind to complementary sequences flanking the target DNA
- 3
- Extension (~72Β°C): Temperature reaches the optimum for Taq polymerase, which extends the primers to synthesize new complementary DNA strands
- 4
After each cycle, the amount of target DNA doubles. Repeated cycles produce billions of copies in a few hours
3. Gel Electrophoresisβ β ββββ± 15 min
Gel Electrophoresis
A laboratory technique that separates DNA fragments by size using an electric current
DNA has a negative charge due to its phosphate backbone, so when an electric current is applied, DNA moves through a porous gel toward the positive electrode. Smaller fragments move faster through the gel pores, so they travel further than larger fragments, resulting in separation by size.
How does gel electrophoresis produce a unique DNA profile for individual identification?
- 1
Non-coding regions of the human genome contain variable number tandem repeats (VNTRs), sequences that repeat different numbers of times in different people
- 2
PCR amplifies these VNTR regions, producing DNA fragments of different lengths depending on the number of repeats
- 3
Gel electrophoresis separates the fragments by size, creating a unique pattern of bands (DNA profile) for each individual (except identical twins)
- 4
Matching banding patterns confirm the DNA sample came from that individual
4. Genetic Modification and GMO Evaluationβ β β βββ± 25 min
Genetically Modified Organism (GMO)
A transgenic organism that has had a gene from another species inserted into its genome to produce a desired trait
Example:
Bt corn has a gene from Bacillus thuringiensis that produces an insect-killing toxin
To create a GMO, restriction enzymes cut the desired gene from the donor genome, and DNA ligase pastes the gene into a plasmid vector. The recombinant plasmid is inserted into a host bacterium, which then transfers the gene to the host organism.
State one benefit and one potential environmental risk of Bt corn
- 1
Benefit: Bt corn produces its own insecticide, so farmers use far less synthetic insecticide. This reduces harm to non-target organisms and lowers production costs, while increasing crop yield.
- 2
Potential risk: The Bt toxin gene can spread to wild related plant species via cross-pollination, creating hybrid plants that may outcompete native species and disrupt local ecosystems. Another risk is harm to non-target insect species like monarch butterflies.
5. Common Pitfalls
Wrong move:
Calling any genetic change a gene mutation
Why:
Gene mutations only affect a single gene; changes to whole chromosomes are chromosome mutations
Correct move:
Always specify the type of mutation by scale (gene vs chromosome) in your answer
Wrong move:
Stating DNA moves toward the negative electrode in gel electrophoresis
Why:
DNA has a negative charge from phosphate groups, and opposite charges attract
Correct move:
DNA moves toward the positive electrode; smaller fragments travel further
Wrong move:
Claiming all mutations are harmful
Why:
Most mutations are neutral, and some produce beneficial traits that drive evolution
Correct move:
Only mutations that disrupt protein function are harmful; mutations are the ultimate source of genetic variation
Wrong move:
Forgetting that Taq polymerase must be heat-stable for PCR
Why:
PCR requires high temperatures to separate DNA strands, which would denature non-heat-stable polymerases
Correct move:
Always link Taq polymerase's heat stability to its function in PCR
6. Quick Reference Cheatsheet
Concept | Key IB Exam Fact |
|---|---|
Mutation types | Gene = 1 gene; Chromosome = whole chromosome change |
PCR purpose | Amplify (copy) small samples of target DNA |
PCR key enzyme | Heat-stable Taq polymerase |
Gel electrophoresis separation | By size: smaller fragments move further |
Gel charge rule | Negative DNA moves to positive electrode |
GMO definition | Transgenic organism with inserted foreign gene |
Bt corn benefit | Reduced insecticide use, higher crop yield |
Bt corn risk | Gene flow to wild plants, harm non-target insects |
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2025 Β· 1
Types of gene mutation
- 2024 Β· 2
PCR and gel electrophoresis
- 2023 Β· 1
GMO benefits and risks
Going deeper
What's Next
Understanding mutation and gene technology builds on your basic genetics knowledge and connects to core IB Biology SL topics, including evolution and human health. Mutations are the ultimate source of genetic variation, which is the foundation of natural selection and speciation, so this topic is critical for understanding evolutionary processes. Gene technology is also a rapidly advancing field with major applications in medicine, including vaccine development and gene therapy for genetic disorders, which links directly to topics on human health and the immune system. Continue your study with the related topics below.