Populations and Evolution

Definitions
1. Population
  1. Group of individuals belonging to the same species living in a particular area
2. Species
  1. Group of similar organisms that can reporduce to give fertile off spring
3. Gene Pool
  1. Complete range of alleles present in a population
4. Allele Frequency
  1. How often an allele occurs in a population
Hardy-Weinberg Principle
1. Predicts that allele frequencies wont change from one generation to the next
  1. Only true if
    1. Large population
      1. That is isolated
        With No Mutations
        And No Natural Selection
        And there is Random Mating
2. Hardy-Weinberg equations used to test whether or not ...
  1. Predicting Allele frequency
    1. p + q = 1
      1. p - Frequency of Dominant allele
      2. q - Frequency of Recessive Alleles
      3. 1 is the entire population
  2. Predicting Genotype Frequency
    1. p^2 + 2pq + q^2 = 1
      1. p^2 is frequency of homozygous dominant
      2. 2pq is the frequency of heterozygous
      3. q^2 is the frequency of Homozygous Recessive
Speciation
1. Evolution of a species from an existing one
  1. Isolation Mechanisms
    1. Geographical
      1. Isolated by geographical barrier
    2. Ecological
      1. Pop dont meet as inhabit different areas
    3. Temporal
      1. Breeding seasons dont coincide
    4. Behavioural
      1. Any mutation that prevents courtship
    5. Mechanical
      1. Physical differences that prevent mating
    6. Gametic
      1. Prevents gametes from meeting
    7. Hybrid sterility
      1. Offspring of different species that are sterile
2. Genetic Drift
  1. Can lead to Speciation
    1. Greater effect in small populations
      1. Where chance dictates
        who survives and breed to pass on alleles
        Rather than environmental factors
3. Two forms of speciation
  1. Allopatric
    1. When a geographical barrier seperates
      1. Two populations of the same species
        If environmental conditions are different between the two populations
        Natural selection will occur to favour optimal alleles
      2. (Oceans, rivers, mountains, deserts)
  2. Sympatric
    1. No geographical barrier
      1. Reproductive isolation still occurs
        Different timings of breeding seasons
        Different location preferences for mating or feeding
        Random mutation can prevent breeding between population
Natural Selection
1. Process
  1. A new mutation arises in the population
    1. Slightly better adapted to the environment
      1. Due to overpopulation, only individuals who are better adapted will survive
        Individuals who survive are more likely to reproduce and pass on the alleles to the offspring
        Better adapted alleles become more common in the population over time
  2. Link to context
Variation in Phenotype
1. Variation due to Genetics
  1. Mutations
  2. Meiosis
    1. Crossover of chromosomes
      1. Independent assortment
  3. Random Fertalisation of gametes
    1. Results in distinct characteristics
      1. Discrete data
2. Variation due to Environment
  1. Amount of light
    1. Infectious diseases
      1. Access to nutrients
  2. Continuous variations in characteristic
    1. Forms a normal-distruibution curve
Effects of different forms of selection on evolution
1. Stabilising Selection
  1. Perserving the average phenotype of the population
    1. Selection against extremes in the population
      1. Usually when environmental conditions are stable
2. Directional Selection
  1. Changes the phenotype to favour phenotype in one direction from the mean population
    1. E.g. Antibiotic Resistant Bacteria
3. Disruptive Selection
  1. Favours extreme phenotypes
    1. At expense of mean phenotype
      1. Mean can split into two extremes
        Due to environmental factors take two distinct forms
        Causes two distinct seperate species

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Graphs To Show Natural Selection (binary/octet-stream)

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Populations and Evolution

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	Created by Dominic Weston about 6 years ago