Heritable Variation and the Sources of Genetic Diversity
Where Variation Comes From
Mutation as the ultimate source
Mutation creates new alleles by altering DNA sequence. Most mutations are neutral or mildly deleterious, but some are beneficial in particular environments. The rate and spectrum of mutation vary across genomes, organisms, and genomic regions.
Recombination and segregation
Sexual reproduction reshuffles existing variation through recombination during meiosis and independent assortment of chromosomes. These processes do not create new alleles, but they create new allele combinations that selection can act on.
Key terms
Common misconception
A mutation is not automatically bad. Whether a mutation helps, harms, or has no effect depends on the environment and genetic background.
Which process creates new alleles rather than just reshuffling existing ones?
Mutation changes DNA sequence and can create novel alleles.
Correct answer: Mutation
Why is recombination important for evolution even though it does not create new alleles?
New combinations can expose favorable or unfavorable interactions among genes.
Correct answer: It produces new combinations of alleles, increasing genetic variation on which selection and drift can act.
Sources of variation compared
| Source | Creates new alleles? | Creates new combinations? |
|---|---|---|
| Mutation | Yes | Sometimes |
| Recombination | No | Yes |
| Independent assortment | No | Yes |
| Gene flow | Sometimes | Yes |
Which statement about heritability is most accurate?
Heritability is a population statistic describing the proportion of variation associated with genetic differences.
Correct answer: It measures how much of trait variation in a population is genetic
Reasoning about variation
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1
Identify the trait or allele being studied.
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2
Determine whether variation is introduced by mutation or redistributed by recombination.
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3
Ask how inheritance will transmit that variation across generations.
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4
Consider whether environmental conditions change the value of the variation.