Chapter 18 - Populations and Evolution

  • Created by: mburgess
  • Created on: 30-01-18 10:23

Key Words: 

  • Gene pool - All the alleles of all the genes within a population at one time
  • Allelic frequency - the number of times an allele occurs within a gene pool
  • Stabilising selection - selection against the extreme phenotypes
  • Directional selection - selection for one extreme phenotype
  • Disruptive selection - favours individuals with extreme phenotypes rather than around the mean of the population
  • Speciation - the evolution of a new species from existing ones
  • Species - a group of individuals that share the same genes and can interbreed to produce fertile offspring

The Hardy-Weinberg Principle 

  • Provides a mathmatical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population
  • The principle makes the assumption that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next and 5 conditions are met
  • There can be no mutations
  • The population is isolated
  • There is no selection - all alleles have an equal chance at going to the next generation 
  • The population is large
  • Random mating

p + q = 1.0

  • p = dominatant allele
  • q = recessive allele
  • 1.0 as the probability of one allele plus the other is 100%

p^2 + 2pq +q^2 = 1.0

  • This equation is used to express it as a probability

Variation in Phenotypes


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