• Created by: Polaris03
  • Created on: 09-11-20 21:33


  • Independent assortment - genes separate independently of each other when gametes are made.
    • Except for linked genes - v close together so more likely to be inherited as a pair, less likely to be separated during recombination.
  • Hemizygosity - no role of dominance and recessiveness (e.g. sex-linked genes).
  • Epistasis - one gene masks another, alleles being masked are hypostatic to the epistatic allele.
    • Often involves pathway where expression of 1 allele is dependent on function of another gene.
    • Recessive epistasis - epistatic allele is recessive, dominant epistasis - epistatic allele is dominant.
  • Population = a group of organisms of the same species inhabiting the same area at the same time.
  • Gene pool = sum of all the alleles in a population.
  • Allele frequency = rate at which a particular allele appears within a population.
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  • Used to compare observed phenotypic ratios w/ expected ratios.
    • Tells you if difference b/w observed and phenotypic ratios are due to chance.
  • Used when:
    • Variation is discrete, not continuous.
    • Data is in whole numbers.
  • Before chi-squared test, a null hypothesis is formed.
    • H0 - There is no significant difference b/w observed and expected data, the difference is due to chance.
    • Chi-squared used to accept/reject null hypothesis.
  • Calculate the degrees of freedom.
    • Degrees of freedom = the number of categories (e.g. phenotypes) − 1.
  • Find the critical value that corresponds to the degrees of freedom in a probability distribution table at 0.05 significance level.
  • χ=ΣE(O−E)2​
    • O = observed values.
    • E = expected values.
  • If chi-squared is lower than critical value accept null hypothesis.
  • Predictions of phenotypic ratios are rarely correct due to random fertilisation.
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Hardy-Weinberg Principle

  • Hardy-Weinberg principle predicts allele frequencies won't change from generation to generation - population's allele + genotype frequencies are inherently stable.
    • Assumes: no mutations, migrations or emigrations; no selective pressure for/against a geneotype; and that the population size is infinite.
    • p+q=1 or p^2+2pq+q^2=1 - p^2=pp = homozygous dominant, q^2=qq=homozygous recessive, etc. 
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