What Is Mutation and Genetic Variation?
Mutations are permanent changes in an organism's DNA sequence, and they are the ultimate source of all genetic variation in populations. Without mutation, evolution would have no raw material to act on.
A mutation is a random, heritable change in a DNA sequence; when mutations create new alleles, they increase genetic variation within a population.
- 1↓DNA Replication ErrorA base is copied incorrectly during cell division
- 2↓Altered DNA SequenceA gene's nucleotide sequence changes permanently
- 3↓New Allele FormedThe changed gene becomes a new version (allele) of that gene
- 4↓Trait Variation AppearsThe new allele may produce a different trait in the organism
- 5Passed to OffspringIf in a gamete, the mutation is inherited and spreads in the population
Step-by-step worked examples
A human genome has about 3.2 billion base pairs. If the mutation rate is roughly 1 in 10^8 base pairs per generation, estimate the number of new mutations per generation.
New mutations = genome size × mutation rate = 3.2 × 10^9 × (1/10^8) ≈ 32 new mutations per generation (order-of-magnitude estimate)
In a population of 500 individuals, a beneficial mutation arises in 1 individual. What is the initial allele frequency (assuming diploid, one new allele copy)?
Total allele copies = 2 × 500 = 1000 New allele frequency = 1/1000 = 0.001 (0.1%)
A point mutation changes a single DNA base from A to G in a gene. Does this always change the protein produced?
The genetic code is degenerate — several codons can code the same amino acid If the mutation falls in the third codon position it may be 'silent' and not change the amino acid If it does change the amino acid, the protein's structure and function may change Conclusion: not every mutation alters the protein — silent mutations are common
Flashcards
Quick quiz
Q1.What best defines a mutation?
Q2.Which type of cell must a mutation occur in to be passed to offspring?
Q3.A mutation that has no effect on the organism's phenotype is called…
Q4.Why is mutation called the 'ultimate source' of genetic variation?
The full card deck, worked steps and AI-tutor support for “What Is Mutation and Genetic Variation?” are in Notek — study by hand before your exam.
Common mistakes
All mutations are harmful or cause disease. — Correct: Most mutations are neutral; only some are harmful and a few are beneficial.
Mutations happen because organisms 'need' them (directed mutation). — Correct: Mutations are random with respect to an organism's needs; natural selection then acts on them.
A mutation in a skin cell will be passed to the next generation. — Correct: Only mutations in germline cells (eggs/sperm) are heritable.
Mutation and genetic variation are the same thing. — Correct: Mutation is a process that creates variation; genetic variation is the resulting diversity of alleles.
FAQ
What is mutation in biology?
A mutation is a permanent, random change in an organism's DNA sequence that can be passed on if it occurs in germline cells.
What causes genetic variation?
Genetic variation comes mainly from mutation (new alleles), recombination during sexual reproduction, and gene flow between populations.
What are examples of mutation?
The sickle-cell allele in humans, coat-color changes in mice, and antibiotic-resistance mutations in bacteria are classic examples.
How is mutation rate calculated?
Mutation rate is typically expressed as new mutations per base pair per generation; in humans it's roughly 1 in 10^8 base pairs per generation.