Evolution

Evolution

1. Darwin's Theory of Evolution

   • Descent with modification
     • EVIDENCE: FINCHES
       • Adaptive Radiation
   • Due to: NATURAL SELECTION
     • 1. Overproduction of Offspring
       • 2. Constancy of numbers
         • 3. Variation within population
           • 4. Struggle for Existance
             • SELECTION PRESSURE
               • Few would live to reproduce
             • 5. Survival Of The Fittest
               • SELECTIVE ADVANTAGE
                 • to reproduce viable offspring
               • 6. Formation of New Species
     • DEFINITION: Tendency for organisms with favourable adaptations to environment to survive and become parents of next generation. It causes to occur as they result in change in allele freq
   • 1. All organisms descent: Remote Common Ancestor
     • 2. New species descended: accumulation of modifications to adapt to new environment
     • 2 IDEAS
   • EVIDENCE SUPPORTING EVOLUTION
     • 1) HOMOLOGY
       • ANATOMICAL HOMOLOGY
         • Similarly of Origin/ Structure and Position
           • Greater the number of homologous structures, closer the two species. Measures evolutionary relatedness
             • 1) Pendactyl limb
               • 5 digit plan at end of limb. Basic structure modified for different functions
                 • Bat wing, dolphin, and mammals
             • 2) Vestigial Organs
               • Remnants, structures less impt for survival now
                 • Snakes: pelvis & hind limbs, whales pelvis & thigh bones,humans: tail bone
             • 3) Ear ossicles
       • EMBRYOLOGICAL HOMOLOGY
         • Similar structures during embryological development. Indicates anatomical homologies
         • More closely related, longer embryological developmt is similar
           • All vertibrates/have pharyngeal pouches in throat
       • Similar structure, different function btw organisms/ indicates evolutionary origin
       • MOLECULAR HOMOLOGY ***
         • Similarities in DNA & A.A seq
         • Two species with same DNA N. Seq = common ancestor
           • More recently branched, more similar
             • Mutations in non-coding region, usually passed on. More silent mutations, more related
               • # Cytochrome C (mitochondria/any aerobic)
                 • Ancient molecule, gene evolve v slowly
                   • Comparing AA- Useful for establishing evolutionary r/s btw distantly related organism
               • Haemoglobin
               • Immune system
                 • Rabbit immune system can produce antibodies tagetting human proteins. Severe pptn
     • 3) BIOGEOGRAPHY
       • Study of past and present geographic distribution of species
       • Single large continent: Pangea but separated by Continental Drift. Evolution affected by Distribution
         • Same area, Looks same but not closely related
           • CONVERGENT EVOLUTION
     • 2) FOSSIL RECORDS

2. II) NATURAL SELECTION

   • I) VARIATION
     • Causes of Variation
       • Mutation:
         • 1. Provides new alleles.
           • 2. Increases Gene Pool
             • 3. Increases Variation
               • 4. Increases phenotypes for Natural Selection to act on
                 • Given: mutation occurs in during GAMETE formation
         • Spontaneous and Random
         • Esp: Asexual
     • Preservation of Variation
       • 1) Diploidy
         • Diploid organisms carry many recessive alleles in heterozygotes
           • Maintains genetic variation in the form of hidden recessive alleles
       • 2) Balanced Polymorphism
         • Presence of >2 phenotypic forms maintained in stable frequencies by Natural Selection
           • 2a) Heterozygote Advantage
             • Heterozygous individuals at particular locus; greater ability to survive and have greater reproductive success
               • due to Selective Advantage
           • 2b) Frequency Dependent Selection
             • Survival and reproduction of any one phenotypic form declines if it become too common in the population. Natural selection tends to favor, whichever phenotype is less common
       • 3) Neutral Variation
         • Genetic Variation does not alter ability of an individual to survive and reproduce and confer no selective advantage
           • Not affected by natural selection
             • Neutral alleles increase/decrease due to chance events (GENETIC DRIFT)
   • acts on INDIVIDUALS

3. NEO-DARWINISM

   • Incorporates principles of genetics
     • New Features
       • Spontaneous Mutation

4. acts on POPULATIONS

   • consists of all individuals of the same species that live in a particular place at the same place
   • Population is the smallest unit that can evolve
     • Microevolution
     • Microevolution is a change in allele frequency in popn
       • Natural Selection affects chances of survival and reproductive success. Along with Gene Flow and Genetic Drift challenges alleles frequencies in popn
   • SPECIATION
     • Emergence of new species
     • GEOGRAPHICALLY separated by PHYSICAL barriers/ cannot interbreed/ REPRODUCTIVELY isolated
       • Within each isolated grp, MUTATION occurs/ natural selection acts
       • Gene pool change in GENETIC composition.
         • NO GENETIC EXCHANGE, speciation occurs
     • ALLOPATRIC SPECIATION
       • population splits/ two geographically isolated
       • Eg. Galapagos Islands
       • habitat fragmentation
         • no gene flow due to geographical barriers/ cannot interbreed even when contact is restored
     • SYMPATRIC SPECIATION
       • single ancestral species/ same geographical location
       • E.g Hawthorn/apple trees and maggot flies
       • no gene flow due to physiological & behavioural isolation/ may be able to interbreed
     • Importance of Islands in speciation
       • Provides many unoccupied niches. Different parts = different selection pressures
         • Few competitors and predators
           • Single species colonizes an area and rapidly diversifies to fill all available niches
             • Island isolate from mainland/ unable to interbreed
               • No gene flow due to geog barriers

5. by CHANGES IN ALLELE FREQUENCY ****

   • CAUSES
     • 1. MUTATION
       • 1. Only source of new genes 2. Increases variation 3. Only mutation in reproductive cells passed to offspring
     • 2. GENE FLOW
       • Reduce differences btw popns
       • Movement of Alleles btw popn due to migration of fertile individuals
     • 3. NATURAL SELECTION
       • Acts on individuals in a popn. Those better adapted to environment are more likely to survive and reproduce. Over many gen, proportion of favourable alleles increase and lead to adaptive change