Evolution

Evolution

1. Theories of evolution

   • Darwin's theory
     • Natural selection (Survival of the fittest): producing ADAPTATION (superior inherited traits) that increase INDIVIDUAL'S FITNESS (ability to survive and reproduce fertile offsprings
       • Postulate 1. Individuals in a POPULATION (SPECIES) vary
       • Postulate 2. Some of these variations are passed onto offspring
         • both genetic and environmental variation can contribute to phenotypic variation
       • Postulate 3. In every generation, some individuals are better able to survive and have more offspring than others due to these inherited variations
       • Postulate 4. Variations the increase survival and reproductive success will abbe a greater chance of being passed not than those do not
     • Descent with modification

2. Hardy Weinberg (Genetic equilibrium)

   • Conditions
     • 1. No natural selection (all traits are neutral)
     • 2. No gene flow (population must be isolated)
     • 3. No genetic drift (population must be large)
     • 4. Random mating (no sexual selection)
     • 5. No mutation
   • Evaluations
     • Allele frequencies for each allele (p, q)
     • Frequency of heterozygous (pq+pq)
     • Frequency of homozygous (p^2, q^2)
     • All alleles sum to 100 % (p+q=1)
     • All individuals sum to 100% (p^2+2pq+q^2=1)
     • Use q^2 and p^2+2pq for each phenotypes

3. Species

   • Macroevolution (Speciation bridges macroevolution⏤evolution on large scale⏤ and microevolution⏤evolution on the small scale)
     • 1. Analogous structures
       • Same in environments and functions, but different common ancestors (independently evolved) and structures. Bird's wings
     • 2. Structural homology
       • Same in structure, anatomy and ancestors, but very different functions
     • 3. Developmental homology
       • All animal embryos start out similar and become less so as embryos matures
     • 4. Genetic homology
       • Similar species have more similar genetic sequences non coding regions
     • 5. Adaptive radiation
       • Single species evolve into different species, and each species diversified into distinct species on different islands
     • Theories of macroevolution
       • Theory 1. phyletic gradualism: evolution occurs by gradual accumulation of small changes. False, since intermediate stages of fossils are missing
       • Theory 2. punctuated equilibrium: evolutionary development goes under short periods of rapid evolution and long periods of stasis (stability) with little or no evolution. Absence of intermediate stages fossils confirms rapid evolutionary events.
   • Definitions
     • 1. Biological species concept
       • Groups of INTERBREEDING natural populations that are REPRODUCTIVELY ISOLATED from others (reproductive isolation between populations, unable to produce fertile offspring)
         • Advantages: Reproductive isolation = evolutionary independence
         • Disadvantages: Not applicable to asexual or fossil species, difficult to assess if populations do not overlap geographically
     • 2. Morphological species concept
       • Morphologically different populations
         • Advantages: Widely applicable
         • Subjective, no clear distinctions
     • 3. Phylogenetic species concept
       • Smallest monophyletic group on phylogenetic tree
         • Advantages: Widely applicable, based on testable criteria
         • Disadvantages: Few well estimated pbylogenies data available
         • 1. Monophyletic group: consists of common ancestors and all of its descendants. also called as clade & lineage
           • Homology: ≈ in organisms due to common ancestors
           • Synapomorphy: shared and derived traits
         • 2. Paraphyletic group (loss of clades or traits)
         • 3. Polyphyletic group: group of organisms that descend from more than one common ancestors
           • Homoplasy: ≈ in organisms due to reasons other than common ancestors

4. Sources of Genetic Variation

   • Mutation
   • Sexual reproduction (gene recombination via crossing over, independent assortment, and random coining of gametes)
   • Heterozygote advantage: heterozygotes have higher chance of survival than homozygous condition (AA, aa), especially in case of autosomal recessive ex) sickle cell anemia

5. Causes of Δof allele frequencies

   • 1. Natural Selection
     • Directional selection
       • Change on mean phenotype (trait) value Usually unchanged trait variance
         • Favors a single phenotype (trait) over the extreme at the other side. After many generations, change in allele frequency is observed. ex) selection of dark moths as a result of pollutions
     • Stabilizing selection
       • No change on mean phenotype (trait) value Decreased trait variance
         • Extremes are not favored, and the most average middle trait is favored. ex) human height
     • Disruptive selection
       • No change on mean phenotype (trait) value Increased trait variance
         • Extremes at both sides are favored, and the most common traits are not favored.
   • 2. Genetic Drift
     • Founder effect: small group of individuals become isolated from a larger px. This results in allele frequency that is different from that of origin. Vulnerable for smaller px.
       • Smaller population size, greater impact of the changes in population
     • Bottlenecks: px undergoes sharp reduction in size due to natural catastrophe. Vulnerable for smaller px.
       • Smaller population size, greater impact of the changes in population
   • 3. Gene Flow
     • Transfer of alleles from populations when individuals emigrate or immigrate populations
   • 5. Mutation (only source of introducing new alleles into px)
     • Point Mutations (Substitution, Insertion, Deletion)
       • Missense: point mutation leading to a codon coding for a different amino acid
       • Nonsense: point mutation leading to a stop codon⏤ UAG, UGA, UAA
         • Translational Codons in Prokaryotes
           • Start (directly behind 5' Untranslated region & ribosomal binding sites): AUG, CUG, GUG, UUG, AUU
             • Initiation of translation: translation initiation factor IF-3 and 30s ribosomal subunit bind to the Shine-Dalgarno sequence of 5' UTR. Then 50s ribosomal subunit is recruited, and the translation begins.
           • Stop: UGA, UAG, UAA
         • Translational Codons in Eukaryotes
           • Start (directly behind 5' Untranslated region): AUG (met), CUG (leucine)
             • Initiating translation
               • Mature mRNA, ribosome, Eukaryotic initiation factors (elFs), GTP, initiator tRNA (Met-tRNA)
                 • Unlike prokaryotes, eukaryotes do not need Shine-Delfarno sequence and modified initiator tRNA (fMet-tRNA)
               • 1. Initiator tRNA (Met-tRNA) gets loaded onto small 40s ribosomal subunit.
               • 2. Eukaryotic initiation factors (elFs) gets loaded as well on the 40s subunit.
               • 3. Pre-initiation complex is formed (40s⏤Met-tRNA⏤elFs).
               • 4. Pre-initiation complex binds to the 5' end of the mRNA (5' Cap).
               • 5. Complex goes through "scanning" of mRNA, ins search for the first AUG.
               • 6. When the first AUG is found, elFs dissociate.
               • 7. Large 60s ribosomal subunit assembles to the COMPLEX at the START CODON
               • 8. INITIATOR tRNA IS PLACED IN THE P SITE OF RIBOSOME, and A site is now available to receive to next charged tRNA
           • Stop: UGA, UAG, UAA
       • Frame shift: inertia or deletion leading to a change in the reading frame of a gene
   • 4. Nonrandom Mating
     • Sexual Selection
       • Intrasexual selection (Competition): male-male competition. mating opportunities are given to the strongest male, and favors traits like muscles, brown, large statures
       • Intersexual selection (Choice): disruptive selection. Female chooses superior males in order to increase fitness of offspring. females invest greater energy so they maximize quality of their offspring, Males increase their fitness by maximizing quantityof their offsprings.
     • Inbreeding (mating with close relatives)
       • Changes GENOTYPE but NOT ALLELE FREQUENCY

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