Microevolution

• Microevolution


  Evolution at the gene level, changes in allele frequency within a population which accumulates through time
• Genetics


  • Provides an explanation on how:
  • Characters changes through time
  • Characters are passed from ancestors to descendants
  • Variation within the population are created
• Allele frequency


  Relative frequency of an allele at a particular locus in a population
• Microevolution is shorter than macroevolution
• Microevolution leads to speciation (macroevolution)
• Genetic information needed for an organism to function, develop, survive, grow, and reproduce

  • Nucleotide - basic building blocks of DNA

  Chromosomes - condensed DNA

  Nucleic acid sequence - succession of bases

  Genes - basic unit of heredity

  
• Gene


  The sequence of nucleotides encodes the synthesis of a gene product
• Allele


  Variant of a gene
• Locus


  Specific location of a DNA sequence in a chromosome

  
• Traits


  • Morphological

  Anatomical

  Physiological

  Developmental

  Behavioral
• Factors that cause change in allele frequency within a population

  • Mutation

  Selection

  Gene Flow

  Genetic Drift
• Hardy-Weinberg Principle


  A principle that the genetic variation (relating to allele and genotype frequency) in a population will remain constant in the absence of disturbing factors

  
• Hardy-Weinberg Equation


  p + q = 1

  p2 + 2pq + q2 = 1

  p = frequency of dominant allele (A)

  q = frequency of recessive allele (a)

  p2 = frequency of dominant homozygous genotype (AA)

  q2 = frequency of recessive homozygous genotype (aa)

  pq = frequency of heterozygous dominant genotype (Aa)

  
• To determine if a population is in Hardy-Weinberg equilibrium, you need at least two generations

  
• Hardy-Weinberg Equilibrium rarely applies in reality as it has to satisfy several assumptions

  
• Mutation


  Alteration of nucleotide sequence in the genome of an organism
• Types of mutation


  • Spontaneous mutation - naturally occurring

  Translesion synthesis - template strand had accumulated damages

  Errors during DNA repair - Non-homologous end joining (NHEJ)

  Induced mutation - exposure to mutagens and other environmental factors

  Single chromosome mutations: Deletion, Duplication, Inversion

  Multiple chromosome mutations: Insertion, Translocation
• Effects of mutation


  • Loss-of-function mutations

  Gain-of-function mutations

  Lethal mutations

  Deleterious mutation

  Advantageous mutation

  Neutral mutation

  Nearly neutral mutation
• Mutation rates are low among organisms, so the effect of mutation on allele frequency is not that large
• Genetic Drift


  Changes in allele frequency due to "chance events" (random sampling events)
• Genetic Drift

  • - Stronger effect on smaller populations
  • Some alleles, even beneficial ones may be lost
  • Alleles may become 100% frequent (fixation)
  • Rare alleles may become more frequent
  • No direction, the effect on allele (whether beneficial or not) are equal
  • Individuals who survived and passed on their genes are not necessarily the fittest
• Natural Selection


  Favors alleles whose effect increases survival/reproductive success
• Bottleneck effect


  A special type of bottleneck event where a small population colonizes a new habitat, may lead to speciation
• Gene Flow


  Movement of genes into and out of a population
• Factors affecting gene flow

  • Dispersal ability or mobility of an organism

  Habitat fragmentation

  Distances between population

  Size of population

  Human-assisted gene flow
• Natural Selection


  Difference in the survival and fitness of organisms, survival of the fittest, environment acting on the phenotype of the organism
• Artificial Selection


  Selective development of preferred phenotype, intentionally targets the preferred phenotype by favoring the preferred genotypes
• More individuals are produced than survive and reproduce (Malthusian competition)
• Organisms have different ability to survive (fitness) and reproduce (differential reproductive success)
• Evolution happens when traits which confer reproductive success are "selected"
• Population

  • Size of population
  • Human-assisted gene flow
  • Frequency of allele and genetic diversity increases in the population where the individual moved
  • Reduces allele frequency and genetic diversity in the original population
• Natural Selection


  • Difference in the survival and fitness of organisms
  • Survival of the fittest
  • Environment acting on the phenotype of the organism
• Artificial Selection


  • Selective development of preferred phenotype
  • Intentionally targets the preferred phenotype by favoring the preferred genotypes
• Favored genotypes


  Genotypes that increase survival in the prevailing environment
• How natural selection works

  1. Basic assumptions about the hypothetical population

  2. Sudden flood wipes-out portion of the population – an example of genetic drift

  3. Populations become separated

  4. An enemy appear. Can move between habitats. Hunts by visual cues

  5. Beetles with unsuitable adaptation (coloration) have a hard time reproducing due to selective pressure from the predator. Survivors able to produce more offspring

  6. Even if the two population intermingles, they will not mate with an individual with a different color – they had been used to mating with individuals that have the same phenotype as them

  7. From an original population with green/brown individuals, two new species arose – pure green and pure brown species
• Factors determining fitness


  • Ability to survive (viability/ survival selection)
  • Ability to reach reproductive age
  • Ability to live for a long period of time
  • Ability to attract mate
  • Ability to produce a number of offspring (fecundity/ fertility selection)
• Fecundity


  Maximum potential reproductive output of an individual
• Fertility


  Actual reproductive potential of an individual
• Semelparity


  • Produces all offspring within a single reproductive event
  • Organisms produces only once and die
• Iteroparity


  • Organisms which reproduce in successive years or breeding seasons
  • Seasonal iteroparity - those with distinct breeding seasons
  • Continuous iteroparity – those that reproduce repeatedly and at any time of the year