Biology - Evolution Chapter 9

• Gene Pool


  all the alleles for genes in that population --> percentage of each allele present will determine characteristics of population

  a change in allele frequencies equal microevolutions
• Factors in changing allele frequencies

  Mutation, Gene Flow, Non Random Mating, Genetic Drift, Natural Selection
• Mutation - change in DNA


  if mutation provides selective advantage it will become more abundant --> more genetic variation = more genetic diversity = greater chance of selective advantage
• Gene Flow


  movement of alleles due to migration

  ex. wolf mates with another population of wolves introducing a new allele in that gene pool --> good because natural selection acts on diversity
• Non Random Mating


  assortative, disassortative, sexual, and inbreeding
• Assortative Mating


  mate with those that look similar --> increases homozygous genotype -->restricts gene flow
• Disassortative Mating


  mate with those that look different --> increases heterozygous genotype --> restricts gene flow
• Sexual Selection


  based on male ornamentation --> females choose a male based on looks (sexual dimorphism) --> impacts allele frequencies
• Inbreeding


  increases homozygous genotypes --> harmful recessive alleles are more likely to appear (purebred animals have higher health incidences)
• Genetic Drift - chance events with a large effect


  the smaller the population = the less likely for parent phenotype to be represented in F2 --> not everyone reproduces so you can lose alleles
• Founder Effect


  change in gene pool when individuals start a new population

  ex. Amish population have a higher chance of six toes because those with five toes have left
• Bottleneck Effect


  disruption causing population to drop --> small sample size remains = inaccurate representation of gene pool --> populate based on remaining alleles
• Natural Selection - affects allele frequencies if it provides selectional advantage

  1. stabilizing selection --> gets ridof extremes focusing on middle ground --> reduces variation
  2. directional selection --> favours one extremes resulting ina shift in phenotypic curve --> common during environmental change
  3. disruptive selection --> favours both extremes and not middle ground --> eliminates intermediate phenotype
• Speciation


  formation of a new species from pre existing species

  when an organism changes it no longer produces viable offspring with original members

  has two gene flow prevention mechanisms --> to inhibit gene flow for long enough can result in two distinct species
• Pre zygotic


  Mating: behavioural, temporal, ecological isolation

  Fertilization: mechanical and gametic isolation
• Post Zygotic


  hybrid inviability, infertility, breakdown
• Behavioural Isolation


  special signals or behaviours that are species specific prevent interbreeding with clsoely related species

  ex. East and West Meadowlarks

  --> different mating songs
• Habitat Isolating


  live in the same ecosystem but different habitats --> no interaction

  ex. common vs northwest garter snakes

  common: in water

  northwest: in open areas
• Temporal Isolating


  occupy same habitat but mating seasons are at different times

  ex. three tropical orchid

  --> bloom for one day but flowering cycles are different (8 days, 9days, . . ) --> reproductively isolated
• Mechanical Isolating


  anatomically incompatible --> genital anatomy is extremely specific and often categorizes different species
• Gametic Isolating


  gametes of different species rarely form a zygote --> sperm may not survive in female reproductive system of a different species
• Hybrid infertility


  genetic incompatibility prevents development of zygote in developmental stage --> prevents mitosis after fusion of gametes
• Hybrid Sterility or Infertility


  barrier when hybrid offspring is sterile --> meiosis fails to produce normal gametes in hybrid due to different chromosome number or structure of parents
• Hybrid Breakdown


  P generation is the hybrid offspring that are viable --> produce F1 generation that is sterile or weak
• Sympatric Speciation


  populations in same habitat diverge genetically --> due to chromosomal changes (plants) or non random mating (animals)

  more common in plants --> cannot split a 3n cell evenly

  sterile offspring could reproduce asexually --> through errors in meiosis steril offspring can reproduce fertile offspring
• Allopatric Speciation


  a population is split into isolated groups by a geographical factor --> gene pool becomes so distinct 2 species cannot interbreed if they are brought back --> can still form a zygote they just don't mate in nature

  small population are more likely to speciate because allele frequencies are unsteady
• Adaptive Radiation 


  diversification fo common ancestral species into variety of adapted species --> type of allopatric speciation --> occurs after evolution of novel characteristics

  ex. wings in insects --> wings resulted in evolution of multiple variations on insect body
• Divergent Evolution


  pattern of evolution in which species become distinct compared to ancestral --> adaptation to different environmental conditions ( sympatric and allopatric)
• Convergent Evolution


  similar traits arise due to different species independently adapting to similar environmental conditions
• punctuated evolutionary change


  evolutionary history of long periods of stasis interrupted by periods of divergence -->first change is a large change --> afterwards they change very little
• gradualism evolutionary change


  change is slow and steady before and after divergence --> big change is result of multiple small changes --> fossil records do not support because species suddenly appear and disappear
• Consequences of human activities on speciation

  fragmented habitats from building roads, building cropland, building tourism areas

  human made barrier may prevent gene flow between split population which may then undergo adaptive radiation --> severely fragmented population may die out if there isn't enough genetic division
• Population Decline


  human activities can cause bottleneck effect and genetic drift --> loss in genetic diversity = inbreeding = declining fertility rates --> populations lacking genetic diversity are more susceptible to new diseases and changes