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7.11 Variations in Populations

Syllabus
2025
Topic
7.11
Level
—

Learning objectives

7.11A—Explain how the genetic diversity of a species or population affects its ability to withstand environmental…Explain how the genetic diversity of a species or population affects its ability to withstand environmental pressures.• The level of variation in a population affects population dynamics.- i. The ability of a population to respond to changes in the envir onment is influenced by genetic diversity. Species and populations with little genetic diversity are at risk of decline or extinction.- ii. Genetically diverse populations are more resilient t o environmental perturbation because they are more likely to contain individuals that can withstand the environmental pressure.- iii. Alleles that are adaptive in one envir onmental condition may be deleterious in another because of different selective pressures.

Genetic Diversity as Population Resilience

Genetic diversity is the variety of alleles within a population. Greater diversity increases the chance that, when the environment changes, some individuals already carry variants that help them withstand the new pressure and reproduce.

Population Response to an environmental perturbation Likely population consequence
High genetic diversity Some individuals are more likely to carry alleles that improve survival or reproduction under the new condition The population is more resilient and more likely to persist
Low genetic diversity Individuals are more genetically similar, so one pressure may affect a large fraction in the same way Decline or extinction risk is higher

During a disease outbreak, a genetically diverse population is more likely to include some less-susceptible individuals. If those individuals survive and reproduce, their alleles become better represented in later generations, helping the population recover.

Allele effect depends on environment: an allele that improves survival under one pressure can be neutral or deleterious under another because the selective pressures differ. Diversity therefore supplies options; it does not guarantee that every variant is useful in every condition.

A population does not create a needed allele in response to a crisis, and every individual does not become more resistant. Resilience comes from preexisting genetic differences and the resulting change in which individuals leave offspring.