Population genetics

• genetic drift occurs due to random chance events that alter allele frequencies in a population
• mutations produce new traits that affect an organism's ability to adapt and survive
• natural selection is the process by which nature selects organisms best adapted to their environment based on traits inherited from their parents or ancestors
• bottleneck effect is when there is a sudden reduction in population size, which leads to loss of variation through genetic drift
• founder effect is where only a small number of individuals establish a new colony/population, leading to an increase in frequency of certain alleles if they happen to be present in those founders
• natural selection is the process by which individuals with advantageous traits are more likely to reproduce, leading to changes in gene frequency over time
• gene flow refers to the movement of genes from one population to another through migration or hybridization
• populations can become isolated from others due to geographic barriers such as mountains, rivers, or oceans
• theory of evolution states that all species are related through common descent and have evolved over time from earlier forms
• evolutionary adaptation refers to changes in gene frequency over time, resulting in genetic variation within populations
• inbreeding depression refers to negative effects on fitness resulting from mating between closely related individuals
• founder effect is when a small group of individuals establishes a new colony, leading to reduced gene pool and increased likelihood of genetic disorders
• gene flow is the movement of genes into or out of a population
• migration can occur within species (intraspecific) or between different species (interspecific)
• species are groups of similar organisms that can interbreed and produce fertile offspring
• microevolution refers to changes in gene frequencies within a single population over time
• sexual selection involves competition among members of one sex to mate with members of the opposite sex
• A population is a group of individuals of the same species occupying the same space/environment and can interbreed
• Genetic variation exists within populations
• Population geneticists study genetic variation within populations and are interested in allele and genotypic frequencies
• Monomorphic genes have a single form, while polymorphic genes have multiple forms
• Human blood types are an example of a polymorphic gene with three blood alleles: I A, I B, I
• Squirrels have one allele for fur color, making them monomorphic for the fur color trait
• The Hardy-Weinberg (H-W) Equation is used to predict genotypic frequencies in a population
• The equation is p^2 + 2pq + q^2 = 1
• p^2 represents the homozygous dominant frequency, 2pq is the heterozygous frequency, and q^2 is the homozygous recessive frequency
• The 5 assumptions for H-W Equilibrium are:

  • No mutation
  • No natural selection
  • Infinitely large population to prevent genetic drift
  • No migration between populations
  • Random mating without sexual selection
• Forces of microevolution include mutation, natural selection, genetic drift, migration, and nonrandom mating
• Practice problems involve calculating allele and genotype frequencies using the Hardy-Weinberg Equation
• Characterizing gene pools numerically
• 5 assumptions for H-W Equilibrium:

  • No mutation
  • No natural selection
  • Infinitely large population (No genetic drift)
  • No migration between populations
  • Random mating (no sexual selection)
• 1. W predicts allele and genotype frequencies stay the same generation after generation when the population is in equilibrium
• Equilibrium means no evolutionary mechanisms are changing the allele or genotype frequencies
• Forces of microevolution:

  1. Mutation

  2. Natural selection

  3. Genetic drift

  4. Migration

  5. Nonrandom mating
• Migration:

  • Gene flow: gene movement among populations
  • Results in increased variation
  • Adjacent populations become more alike
• Genetic Drift:

  • Allele frequencies may "drift" randomly from one generation to the next
  • Decreases genetic diversity
  • Two types: Founder effect and Bottleneck effect
• Genetic Drift: Founder Effect

  • A few individuals disperse and become founders of a new, isolated population
  • Rare alleles in the parent population may become more common in founder populations
• Genetic Drift: Bottleneck Effect

  • Event reduces population size = Permanent loss of alleles
  • Example: Textbook before and after drought scenarios
• Mutation:

  • Random changes in the genetic material of an organism
  • Mutations may be harmful, neutral, or beneficial
  • Only inherited mutations may lead to evolution
• Natural Selection:

  • Process in which heritable traits that provide a survival or reproductive advantage become more common in successive generations
  • Selection favors certain phenotypes
  • Individuals with greater "fitness" are more likely to survive and reproduce