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Section 7 - Genetics, populations, evolution, and ecosystems - Coggle…

- - - - Phenotype = the observable characteristics of an organism
      - Phenotype is the result of the interaction between the genotype and the environment
      - Genotype = the genetic constitution of an organism
    - - Need large samples to see ratios
      - Monohybrid crosses
        
        Inheritance of a single gene
        
        Example - crossing one gene with dominant and recessive alleles
      - Dihybrid crosses
        
        Inheritance of two genes
        
        Independent assortment - each allele from a pair can combine randomly with another allele from another pair
      - Multiple alleles
        
        Example - ABO blood groups
        
        A and B are co-dominant, whereas O is recessive to both
      - Sex-linkage
        
        A gene carried on the X or Y chromosome
        
        XY = male
        XX = female
      - Autosomal linkage
        
        Two or more genes present on the same chromosome (but not on sex chromosomes)
      - Epistasis
        
        One allele masks the expression of another allele of another gene in the phenotype
        
        Example - coat colour in mice - white, black, agouti
      - Chi-squared test
    - - Allele = different form of a gene
        
        Only one allele is found at the locus for a particular gene
        
        The two alleles can be homozygous or heterozygous
        
        Two loci, as there are two homologous chromosomes in diploid cells
        
        There can be many alleles of one gene e.g. ABO blood groups
      - Dominant
        
        Only one allele needed to express the phenotype
      - Recessive
        
        Only expresses the phenotype if there are two recessive alleles
        
        Homozygous recessive
      - Co-dominant
        
        Both alleles are expressed and contribute to phenotype
- - - - Gene pool = all alleles of all genes in a population
      - Allele frequency = how common one particular allele is in the gene pool
    - - Species can exist as one population or multiple populations
      - Population = group of organisms of the same species in one area at a time
        
        Can interbreed
    - - Predicts that allele frequencies (proportions of dominant and recessive) will not change from generation to generation
      - p^2 + 2pq + q^2 = 1
        
        p is the frequency of the dominant allele, q is the frequency of the recessive allele
      - Conditions
        
        A large population
        
        No new mutations
        
        Random mating within the population
        
        No selection of particular alleles
        
        Isolated population, so there is no flow of alleles in or out of the population
  - - - Wide variation in phenotype in a population
      - Due to genetic and environmental factors
      - Sources of variation
        
        Gene mutation
        
        Meiosis
        
        Random fertilisation of gametes (producing new combinations)
      - Variation must be present for selection to occur
    - - Populations are separated from each other
        
        Allopatric speciation
        
        Geographical separation
        
        Sympatric speciation
        
        Subpopulations are in the same geographical area
        
        Selection within each subpopulation
        
        Changes in allele frequency in each subpopulation
        
        New species form
        
        Cannot interbreed with the other species
      - Genetic drift in small populations
        
        Faster development of a new species
    - - Selection pressures are factors that limit the population
        
        Predation
        
        Disease
        
        Competition for resources
        
        Intraspecific competition
      - Results in the better-adapted individuals surviving and reproducing
        
        They pass on the advantageous alleles to the next generation
        
        Changes allele frequency in the gene pool of the population over time
        
        Evolution
      - Types of selection
        
        Directional selection
        
        Mean phenotype shifts to left or right, one extreme is selected for
        
        Antibiotic resistance in bacteria
        
        Disruptive selection
        
        Both extremes are selected for, generating two subpopulations
        
        Stabilising selection
        
        Selects against extreme phenotypes, favours the average
        
        Human birth weights
- - - - Habitat = the place where an organism lives
        
        Ecosystems contain many habitats
      - Ecosystem = the community and the non-living components from the environment
        
        Ecological niche = how an organism fits into its environment e.g. interactions, role
        
        The niche is determined by how the organism is adapted to abiotic and biotic factors
      - Community = the populations of different species in one place at a time
        
        Population size depends on abiotic factors, competition, and predation
    - - For slow-moving or non-motile organisms
        
        Quadrats
        
        Randomly placed
        
        Use a random number generator to obtain coordinates
        
        Frequency or percentage cover
        
        Systematic sampling along a belt transect
      - For motile organisms
        
        Mark - release - recapture
        
        Mark must be non-toxic and not make the organism more visible to predators
        
        Proportion of marked to unmarked stays constant
        
        The mark must stay on the organism
        
        No births or deaths within population
        
        Even ditsribution of marked organisms
    - - Primary succession = changes in the species present in a barren area
      - Pioneer species
        
        Colonises an inhospitable environment e.g. bare rock or sand dunes
        
        Pioneer species die and release nutrients into the land
        
        This allows plants to grow and changes the abiotic environment, making it less hostile
        
        More habitats and niches to support more species
        
        Climax community
        
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      - Succession us managed to conserve habitats