Variation and evolution

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  • Variation & Evolution
    • types of variation
      • variation is the differences that exist between individuals.
      • variation within species=intra specific, variation between different species= inter specific
      • dicontinuous- 2 or more distinct catagories, data is qualitative, (words)
        • different alleles on a single locus have a large effect on the phenotype. environment has no effect.
      • continuous variation- when the individual in a population vary within a range. data is quantitative (numbers)
        • each gene has an additive effect to the phenotype, these are polygenes from different chromosomes the environment has some effect.
    • phenotypic variation
      • variation in the phenotype
      • 1) different species have different genes, the same species have same genes, different alleles.
        • these alleels make up the genotype and differences in the genotype cause variation in phenotype
      • 2) variation can be caused by environment
        • characteristic controlled by environmental factors can change over a lifetime
      • 3) variation can be caussed by both genotype and environment.
        • eg plant heigh depends on genes, and nutrients and space etc
      • characterisitcs controlled by one gene are mongenic
    • alleles
      • complete range of alleles in population is the gene pool
      • how often a specific allele occurs is allele frequency
    • natural selection
      • 1:new alleles are caused by random genetic mutation
      • 2: if allele is advantageous they will survive under selection pressures
      • 3: survive and reproduce and pass on allele
      • 4:over many generation this allele is passed on, increasing frequency, causing evolution. this is directional selection
    • genetic drift
      • 1: by chance, one allele is passed on to offsrping. allele frequency increases
      • 2: over time this will lead to evolution
      • 3: this allele has no effect on the survival of the organism
      • genetic drift is more effective in smaller populations, and when there is a bottle neck


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