What is Genetic Variation in Populations?
Genetic variation is the diversity of alleles and genotypes among individuals in a population — the raw material evolution acts on. Without it, populations cannot adapt to changing environments, resist new diseases, or evolve over time.
Genetic variation refers to differences in DNA sequences among individuals in a population, arising mainly from mutation, recombination (crossing over), independent assortment, and gene flow.
- 1↓MutationRandom changes in DNA sequence create entirely new alleles — the ultimate source of all genetic variation.
- 2↓Recombination (Crossing Over)Homologous chromosomes exchange segments during meiosis, creating new combinations of existing alleles.
- 3↓Independent AssortmentChromosome pairs separate randomly into gametes during meiosis, shuffling allele combinations.
- 4Gene Flow (Migration)Individuals moving between populations introduce new alleles, increasing variation within a population.
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Step-by-step worked examples
A locus has two alleles: A (frequency 0.6) and a (frequency 0.4). Calculate the expected heterozygosity.
H = 2pq = 2 × 0.6 × 0.4 H = 0.48 (48% of individuals are expected to be heterozygous)
In a population of 500 individuals, 50 new mutations arise at a locus in one generation. Calculate the per-individual mutation rate.
Mutation rate μ = new mutations ÷ population size μ = 50 ÷ 500 = 0.1 mutations per individual per generation
Two populations exchange migrants: 20 individuals move into a population of 200 each generation. Calculate the migration rate (m).
m = migrants ÷ total population m = 20 ÷ 200 = 0.10 (10% migration rate)
Flashcards
Quick quiz
Q1.Which of the following is a source of genetic variation?
Q2.What happens to genetic variation during a population bottleneck?
Q3.Crossing over during meiosis increases genetic variation by...
Q4.A locus has allele frequencies p = 0.7 and q = 0.3. What is the expected heterozygosity (2pq)?
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Common mistakes
Thinking genetic variation and genetic drift are the same thing. — Correct: Genetic variation is diversity itself; genetic drift is a process that changes (usually reduces) that diversity by chance.
Believing mutation is always harmful. — Correct: Most mutations are neutral, some are harmful, and a few are beneficial — mutation is the ultimate source of all new genetic variation.
Assuming small populations have the same genetic variation as large ones. — Correct: Small populations lose genetic variation faster due to genetic drift and inbreeding.
Believing gene flow always increases variation within a population. — Correct: Gene flow increases variation within a population but tends to decrease differences between populations.
FAQ
What is genetic variation?
It is the diversity of alleles and genotypes among individuals in a population, arising from mutation, recombination, and gene flow.
What causes genetic variation in populations?
Mainly mutation, recombination during meiosis (crossing over and independent assortment), and gene flow between populations.
Why is genetic variation important for evolution?
It is the raw material natural selection acts on — without it, populations cannot adapt to a changing environment.
How is genetic variation measured?
A common measure is expected heterozygosity (H = 1 − Σpᵢ²), the probability two randomly chosen alleles at a locus differ.