D1.3 Mutations and Gene Editing
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What is a mutation?
A permanent change in the DNA sequence of an organism.
When do mutations most commonly occur?
During DNA replication.
What is a point mutation?
A mutation affecting one nucleotide/base pair.
Types of point mutations?
Substitution Insertion Deletion
What is a SNP?
Single Nucleotide Polymorphism – variation at a single base position.
What are INDELS?
Insertions and deletions of nucleotides.
What is a frameshift mutation?
Insertion/deletion not in multiples of 3 → shifts reading frame.
Why are frameshift mutations usually severe?
Alter all downstream codons Change entire amino acid sequence Often produce nonfunctional proteins
What is a substitution mutation?
One base replaced with another.
Effects of substitution mutations?
Silent (no change) Missense (different amino acid) Nonsense (STOP codon)
What are mutagens?
Agents that increase mutation rate.
What causes mutations?
Errors in DNA replication Mutagens (e.g. UV radiation, chemicals)
What proportion of mutations are harmfull?
Most are neutral or harmful, few are beneficial.
What is a beneficial mutation?
Increases fitness → more likely to be passed on.
What is a harmful mutation?
Reduces fitness → selected against.
Why are mutations important?
They are the only source of new alleles → genetic variation.
Why might silent mutations still matter?
Can affect: mRNA stability transcription efficiency protein folding speed
What is a silent mutation?
Mutation that does not change phenotype.
How many new mutations does a human typically have?
~200–300 new mutations per generation.
What are somatic mutations?
Occur in body cells → not inherited.
What are germ-line mutations?
Occur in gametes → inherited.
``` Consequences of somatic mutations?
Affect only part of organism Can cause diseases (e.g. cancer)
Consequences of germ-line mutations?
Present in all cells of offspring Passed to next generation
Why do germ-line mutations drive evolution?
They are heritable, so natural selection can act on them.