The Hardy-Weinberg Principle
G. H. Hardy Wilhelm Weinberg
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Wilhelm Weinberg was a German physician who developed an interest in population genetics during his practice. He was curious about Mendel's work and the statistical probabilities of dominant and recessive trait inheritance. G. H. Hardy was an English mathematician who studied the mathematical patterns in allele frequencies. Weinberg and Hardy did not collaborate, but collectively their work has become a standard for studying changes in gene pools.
To help us determine if the gene pool of a population does change, the Hardy-Weinberg Principle states conditions where no change takes place. It may seem an odd approach, but it actually sets a standard by which change can be measured. According to the Hardy-Weinberg Principle, five conditions must be in place for a population to maintain a stabilized or unchanging gene pool. When a gene pool is stable, evolution is not taking place.
Five Conditions For a Non-evolving Population
- The population size must be large. (The effects of change on the gene pool of a small population can be dramatic.)
- There can be no migration either into or out of the population. (Variation in a population can change as new organisms of the same species move about.)
- No mutations occur. (Mutation leads to variation.)
- Mating is random. (Mate selection is usually based on phenotypic expressions of physical traits or behaviors, meaning that members of a population do not have equal chances of mating.)
- Natural selection does not take place. (Selection pressures such as predator/prey relationships or environmental changes modify the gene pool.)
The conditions described above are only half the story. The real tool for studying gene pool changes is called the Hardy-Weinberg Equilibrium. Watch the video below for a tutorial on how mathematics is used to study evolution as it applies to genetics.