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Chapter 17 (rates of evolution (mutations (If a feature becomes…

- - - - mutations will disrupt development
      - these mutations become advantageous
      - disruptive mutations outnumber constructive
- - - - 1 species becomes so changed its considered different
      - millions of years to evolve #
      - new beneficial allele has to spread to entire population
      - gene flow is physical movement of alleles
      - pollen transfer
        
        all alleles are present in plants pollen grain
        
        pollen grains carry 1 full haploid genome
        
        new alleles can travel to distant plants
        
        possible rapid allele movement
      - seed dispersal
        
        some plants drop fruit/seeds close by
        
        some plants have long-distance dispersal mechanisms
        
        seeds can be dispersed by weather
        
        carried by wind
        
        flood dispersal
        
        stream flow
        
        spiny and gummy stick to creatures
        
        migratory animals can carry seeds far
      - vegetative propagation
        
        plants can produce small mobile peices
        
        these pieces reproduce vegetatively
    - - species splits and half evolve into 2nd species
      - occurs when species don't stay homogeneous
      - reproductively isolated
        
        happens to species in 2 separate regions
        
        if alleles arise in one region but not other
        
        start reproducing differently
      - abiological reproductive barriers
        
        any physical, nonliving feature
        
        prevents two populations from exchanging genes
        
        original species physically divided into 2
        
        if speciation results, its called either
        
        allopatric
        
        geographic speciation
        
        example of barriers
        
        mountain rages
        
        rivers
        
        deserts
        
        oceans
        
        valleys
      - biological reproductive barriers
        
        any biological phenomenon
        
        preventing successful gene flow
        
        discriminating pollenator
        
        very picky about what it chooses to pollinate
        
        reasons- flower color, shape, or fragrance
        
        muatations
        
        can cause pollinators to be confused
        
        could cause recognition issues
        
        timing of flower
        
        flowers open at night vs day
        
        cant interbreed with flowers opening other times
        
        when plant decides to flower
        
        sympatric speciation
        
        two groups growing together
        
        become reproductively isolated anyways
        
        prezygotic internal isolation mechanisms
        
        they act before zygotes are formed
        
        reproductive barriers preventing pollen from moving
        
        postzygotic internal isolation barriers
        
        genomes being too different
        
        hybrid sterility
        
        earliest postzygotic barrier to arise
        
        species allowed to breed
        
        offsprings seeds are sterilized
  - - - normally due to new habitat
      - no competition existing
      - no environmental stress
    - - first species
      - if only 1 founder, there's small gene pool
    - - small gene pool means easy influence
      - small populations subject to more accidents
      - gene pool can change rapidly and erratically
- - - - 2 parents with 2 different gene patterns
      - crossing over causes variation
      - variation causes genetic diversity
    - - created by different individuals
      - all alleles in individuals sex cells
    - - Mutations
        
        all genomes subjected to mutagenic factors
        
        mutation causes new alleles
        
        significance depends on population size
      - Accidents
        
        accidents are unadaptable situations
        
        phenomena qualify as accidents
        
        can wipe out area of mutation
        
        could wipe out entire alleles
        
        impacts future generations
      - Artificial Selection
        
        humans purposely change allele frequency
        
        selective breeding
        
        influences gene pool
        
        used to create perfect plants/clones
      - Natural Selection
        
        most important factor changing gene pool
        
        survival of the fittest
        
        individuals most adapted survive
        
        2 conditions before natural selection occurs
        
        offspring
        
        population must produce offspring
        
        must have too many offspring for all to live
        
        offspring then compete for space/resources
        
        progeny
        
        progeny must differ from each other
        
        alleles must be different
        
        that way fungus cant wipe all out
        
        if all are same, natural selection wont occur
      - factors not part of natural selection
        
        purpose, intention, planning
        
        voluntary decision making
        
        plants don't make decisions. natural selection does
        
        situations in which natural selection does not operate-
        
        if which individuals are same
        
        impossible to adapt
        
        survival being universal
- - - - earth condensed from gas and dust
      - atmosphere mostly hydrogen 4.6 bil. years ago
        
        hydrogen is light, most lost in universe
        
        replaced by a second atmosphere
        
        second atmosphere released from rock matrix
        
        provided hydrogen sulfide, water, ammonia,
        
        methane
        
        all found in volcanic gases
        
        found in meteorites
        
        rock matrix was composing earth
        
        heavy bombardment by meteorites
        
        second atmosphere was a reducing atmosphere
        
        due to lack of molecular oxygen
        
        presence of powerful reducing agents
    - - early 2nd atmosphere exposed to powerful energy
      - intense UV and gamma radiation from sun
        
        these radiations have energetic quanta
        
        energetic quanta knock electrons from atoms
        
        creating highly reactive free radicals
      - heat powered reactions
        
        coalescence of gas and dust was a heat source
        
        2nd heat source radioactive decay
    - - time available for chemosynthetic origin had no imits
      - due to lack of free molecule oxygen
      - without oxygen, nothing to breakdown chemicals