Genetics OCR Biology A2

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  • Created by: Erin
  • Created on: 03-05-15 21:35
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  • Genetics
    • Genotype
      • Genetic makeup of an organism
      • Determined by genotype and environment
        • e.g. Humans intelligence is partly determined by genes and partly environment - got genetic potential? must be placed in stimulating learning environment
    • Phenotype
      • Physical appearance of a genotype
      • Determined by genotype and environment
        • e.g. Humans intelligence is partly determined by genes and partly environment - got genetic potential? must be placed in stimulating learning environment
    • Codominant
      • Characteristic where both alleles contribute to the phenotype
    • Linkage
      • refers to 2 or more genes that are located on the same chromosome
      • Reduces the number of phenotypes resulting from a crossover
        • If genes re linked,  during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
          • The linked alleles are more than likely than expected to be inherited together
            • So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
              • Reduces the number of phenotypes resulting from a crossover
                • If genes re linked,  during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
                  • The linked alleles are more than likely than expected to be inherited together
                    • So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
      • Epistasis
        • The interaction of different gene loci so that 1 gene locus masks or suppresses  the expression of another gene locus
        • The homozygous presence of a recessive allele (1) may prevent the expression of another allele (2) at a second locus
          • The alleles at the first locus (1) are EPISTATIC to the alleles at the second locus (2), which are hypostatic
        • is not INHERITED, it is an interaction between the 2 gene loci - it reduces phenotypic variation
        • Recessive epistasis
          • F2 Generation 9:3:4
            • 9 - both dominant
            • 3 - dominant, epistatic, other recessive
            • 4 - recessive epistatic
          • Cross  homozygous recessive parent with a homozygous dominant parent
            • F2 Generation 9:3:4
              • 9 - both dominant
              • 3 - dominant, epistatic, other recessive
              • 4 - recessive epistatic
        • Dominant epistasis
          • 13:3
          • 12:3:1
            • crossing a homologous recessive parent with a homologous dominant parent
            • 12 - dominant epistatic
            • 3 - recessive epistatic dominant
            • 1 - both recessive
        • 'Complementary fashion'
          • 1) Cross 2 strains of white-flowered sweet peas - all F1 generation have purple flowers
            • 2) Interbreed F1 generation. F2 generation 9:7
              • Untitled
      • Chi-squared test
        • statistical test to find out the difference between observed categorical data and expected data is small enough to be due to chance
        • Conditions
          • 1) relatively large sample size              2) Only raw counts         3) there are no zero scores
      • Variation
        • Intraspecific variation - within a speceis
        • Interspecific variation = between different species
        • Discontinuous Variation - qualitative differences between phenotypes. No intermediate categories
        • Continuous Variation - quantitative differnces between phenotypes - wide variations within a population no distint categories

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