Unit 1 Evolution

• Struggle in accepting evolution as this tested loyalty to God → went against the common idea at the time that animals remained the same throughout their lifetime and God made animals the same throughout their lives
• Evolution


  The process of organisms changing over time as a result of obtaining stronger survival characteristics
• Traits evolutionary biologists might study

  • Physical Characteristics
  • Behavioral Traits
  • Genetic characters
• Darwin's theory of evolution

  Observed Evolution as descent with modification by means of Natural Selection -> all animals/organisms are related to each other
• Patterns Darwin observed


  • Change over time
  • Change over geographic distance
  • Resemblance to fossils
  • Homology
  • Vestigial Traits
• Requirements for adaptive change in a population

  • Variation
  • Heritability
  • Differential Survival or Reproductive Success
• Heritability


  The process of inheriting traits that are fit for success/survival in the environment
• Inherited


  Traits that are passed down from one generation to another through genetic transmission
• Phylogeny


  Model/hypothesis of branching relationships of populations that give rise to multiple descendant populations → data comes from observable traits
• MRCA (most recent common ancestor)

  Most recent node from which the set of tips of interest descend
• Clade


  A collection of branches that stem from an ancestor and includes all of its descendants — there can be multiple clades
• Paraphyletic Group


  Phylogenetic tree that doesn't contain all descendants of the MRCA
• Most parsimonious model


  The species that requires the least evolutionary changes
• Homologous


  Derived from the same ancestor
• Analogous


  Shared from the same environments
• Hardy-Weinberg Equilibrium


  Null model that assumes relationship without any evolutionary forces acting on it
• Genotypes


  • AA
  • Aa
  • aa
• Alleles


  • A
  • a
• If the observed genotypic frequency is higher/lower than the calculated Hardy-Weinberg genotypic frequency, than the population is not under Hardy-Weinberg equilibrium
• Fitness


  The ability of an individual to survive and reproduce in its environment
• Relative Fitness


  Absolute fitness (fraction that survived of total pop) / highest absolute fitness
• Selection coefficient can be calculated by using the relative fitness → 1-s (selection coefficient) = relative fitness
• p'


  Frequency of allele A after one generation of selection
• If an allele is rare, the allele would eventually increase rapidly
• If selection is acting against a rare dominant or rare recessive allele, evolution will act on this by:

  • When a dominant allele is rare, natural selection will lower its frequency rapidly
  • When a recessive allele is rare, these alleles will be hidden in heterozygotes allowing them for slow growth (hides from selection)
• How evolution acts on rare dominant vs rare recessive alleles

  • Rare dominant allele: natural selection will lower its frequency rapidly
  • Rare recessive allele: these alleles will be hidden in heterozygotes allowing them for slow growth (hides from selection)
• When A is dominant, it increases rapidly initially until it becomes common in the population, that is when growth reaches a plateau
• When A is recessive, it takes a while to increase in frequency; however, when it soon becomes common, that is when it increases rapidly
• p^


  p at equilibrium meaning the value of p after a change of 1 generation of selection
• Frequency-dependent selection


  The fitness of each genotype depends on whether its rare or common
• In the Luria-Delbruck Experiment, they found that the mutations happened spontaneously before selection was even applied
• Mutations can NEVER be lost by selection
• Forward - Backward mutation


  (A → a) at rate µ
• In the case that there is a deleterious allele with a selective disadvantage, under mutation selection balance, the allele would be present at a higher equilibrium frequency when it is recessive because it can still hide out in recessive genotypes
• Mutation changes allele frequencies SLOWLY and is much slower than natural selection
• Mutation adds NEW alleles every generation
• Mutation tends to work against selection
• Antibiotics are only effective for bacteria and not viruses
• Antibiotic Resistance


  Describes the increase in bacterial colonies resistance to antibiotics through natural selection
• Kinds of Antibiotic Resistance

  • Germs develop new cell processes that avoid using the antibiotic's target
  • Germs change or destroy the antibiotics with enzymes, proteins that break down the drug
  • Germs restrict access by changing the entryway or limiting the number of entryways
  • Germs change the antibiotic's target so the drug can no longer fit and do its job
  • Germs get rid of antibiotics using pumps