Rucete ✏ Campbell Biology In a Nutshell
Unit 4 MECHANISMS OF EVOLUTION — Concept 23.2 The Hardy-Weinberg Equation Can Be Used to Test Whether a Population Is Evolving
The Hardy-Weinberg equation is a fundamental tool used to assess whether evolutionary change is occurring within populations. By comparing observed genotype frequencies to those predicted under conditions of no evolution, biologists can determine if allele frequencies are changing.
Gene Pools and Allele Frequencies
- Gene pool: All copies of every type of allele at every locus in a population.
- Fixed allele: Only one allele exists at a locus; all individuals are homozygous.
- Allele frequency: Proportion of a specific allele within the gene pool.
- Example: In a flower population with 1,000 alleles, if 800 are Cʀ, then frequency of Cʀ = 0.8.
Hardy-Weinberg Equilibrium (HWE)
- HWE: A state where allele and genotype frequencies remain constant generation after generation, assuming no evolutionary influences.
- Equation: p² + 2pq + q² = 1
- p²: Frequency of homozygous dominant genotype.
- 2pq: Frequency of heterozygous genotype.
- q²: Frequency of homozygous recessive genotype.
- Populations in HWE are not evolving.
Conditions for Hardy-Weinberg Equilibrium
Five conditions must be met for a population to remain in equilibrium:
- No mutations: Gene pool remains unchanged.
- Random mating: No selective mating or inbreeding.
- No natural selection: Equal survival and reproduction chances.
- Extremely large population size: Prevents genetic drift.
- No gene flow: No migration of alleles between populations.
Violation of any of these conditions typically results in evolution.
Applying the Hardy-Weinberg Equation
- The equation helps test if a population is evolving.
- Example: PKU (a recessive genetic disorder) occurs in 1 out of 10,000 U.S. births.
- Using HWE, scientists estimate about 2% of the population are heterozygous carriers.
- Helps estimate disease carrier rates for medical genetics.
Importance of Hardy-Weinberg Equilibrium
- Acts as a null hypothesis for testing evolutionary change.
- Helps identify which evolutionary forces (selection, drift, mutation, gene flow) are active.
In a Nutshell
The Hardy-Weinberg equation is a valuable tool to determine whether a population is evolving. Deviations from equilibrium indicate evolutionary forces like selection, drift, or gene flow, driving changes in allele and genotype frequencies across generations.