Chapter 23 Quizzes: Self Activities Chapter Cum. Videos   Movies    Words   Appendix    Summary   Art    Art 

Unit 4: Mechanisms of Evolution The Evolution of Populations Review Notes Med Choi Fill
  1. Natural selection acts on individuals, but populations evolve, based on genetic variations, the change in genetic makeup of a population over time is called microevolution .
     
     
  2. A population is a localized group of individuals that are capable of interbreeding and producing fertile offspring.
     
     
  3. As a population evolves, its allele and genotype frequencies change. Such evolutionary change can be analyzed by comparing it to a non-evolving population.
     
     
  4. A non-evolving population reaches the Hardy-Weinberg equilibrium due to Mendelian segregation of alleles, under five idealized conditions:
       
       
    • Extremely large population size.
    • No gene flow due to migration.
    • No mutations .
    • Random mating.
    • No natural selection .
     
     
  5. Mendelian inheritance preserves allele frequencies in a population, resulting in constant genetic variation.
     
     
  6. At Hardy-Weinberg equilibrium, the distribution of 2 alleles p and q in a population can be modeled by these equations:
       
       
    • The allele frequencies are described by p + q = 1, where p is the dominant allele frequency and q is the recessive allele frequency.
       
       
    • The genotype frequencies are described by p2 + 2pq + q2 = 1.
     
     
  7. Mutation and sexual recombination produce the variation that makes evolution possible.
       
       
    • Genetic drift in small populations result tends to reduce genetic variation. In very small populations the bottleneck effect can contribute to severe loss of genetic diversity.
       
       
    • Gene flow from the movement of individuals or gametes between populations can affect allele frequencies and tends to reduce genetic differences between populations.
       
       
    • Mutation is the basis for natural selection, and results in unequal reproduction of alleles.
       
       
    • Selection favors certain genotypes by acting on the phenotypes of individuals.
         
         
      • Directional selection favors individuals at one end of the phenotypic range.
         
         
      • Disruptive selection favors individuals at both extremes of the phenotypic range.
         
         
      • Stabilizing selection favors intermediate phenotypes.
       
       
    • Summary.
     
     
  8. Heterozygotes sometimes may possess greater fitness than homozygotes and preserve a recessive allele in a population due to heterozygote advantage.
     
     
  9. In many species females are choosy in selecting their mates, resulting in sexual dimorphism . This is called intersexual selection, or mate choice.
     
     
  10. Intrasexual selection is the competition among males for access to mates, often at the peril of their own survival.