Inherited Change

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  • Inherited Change
    • Studying inheritance
      • Genotype
      • Phenotype
      • Homologous chromosomes
    • Monohybrid inheritance
      • Genetic crosses
        • As per GCSE
      • Gregor Mendel
        • Study of inheritance in pea pod colour
      • Law of segregation
        • In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete
      • 3:1
    • Probability and genetic crosses
      • Actual results of genetic crosses rarely same a s predicted
        • Each outcome due to chance
        • Larger the sample, more likely actual results are to come near to theoretical
    • Dihybrid inheritance
      • When 2 characters determined by 2 different genes located on different chromosomes
      • 9:3:3:1
      • Law of independent assortment
        • Each member of a pair of alleles may combine randomly with either of another pair
    • Codominance and multiple alleles
      • Codominance
        • Both alleles are expressed in the phenotype
        • Snapdragon flower colour
        • 2:1:1
      • Multiple alleles
        • Human ABO blood groups
        • When there's >2 alleles, of which only 2 may be present at the loci of an individual's homologous chromosomes
    • Sex-linkage
      • X and Y chromosomes are different shapes and sizes
      • eg. haemophilia
        • Much more common in males
          • only need one defective X chromosome, females need two
          • Females often die at start of menstruation
      • Pedigree charts
        • Square = male. Circle = female. Shaded = affected
    • Autosomal linkage
      • When two or more genes are carried on the same autosome
      • 3:1
    • Epistasis
      • Arises when the allele of one gene affects or masks the expression of another in the phenotype
      • eg. Albino. 9:4:3 in mice.
        • If the pigment melanin isn't coded for, then the other alleles in the phenotype can't be expressed.
      • Or where genes act in a sequence by determining the enzymes in a biochemical pathway. If one enzyme is non-functional another may not be expressed.
    • Eugenics (1883 - 1940)
      • Example of how genuine scientific research and knowledge can be interpreted wrongly and used for bad.
      • Made famous by the Nazis, but all across Europe and the USA at the time there were many laws promoting eugenic values and racial cleansing.
    • Chi-squared test
      • (O-E)^2/E
        • O = observed values
        • E = expected values
      • Degrees of freedom. Critical values
      • If the value for chi-squared is greater than the critical value, then the results are statistically significant


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