DNA Profile Interpretation

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  • DNA Profile Interpretation
    • Once a DNA profile match has been made, the significance of the match has to be estimated.
      • Need to estimate the frequency of a DNA profile
        • Need experience to reliably interpret DNA profiles, especially those that are degraded and have low levels of DNA
        • Requires knowledge of population genetics and some statistical analysis of data
          • Essential to understand where the profile comes from in order to assess the strength of a  match
          • A population can be described as a group of people sharing common ancestry.
            • it is not possible to estimate allele frequencies from the whole population as this would require testing everybody
              • Population databases therefore represent a subset of the population
        • Estimate how rare or common a DNA profile may be
      • When a match is found, the probability that a second copy of the DNA profile will be present in a certain population is determined.
        • Random Match Probability
        • Likelihood Ratio
    • Hardy-Weinberg Equilibrium
      • If a random person is picked from the population, we can calculate the probability that they will have a particular genotype
      • Condition that occurs when the frequency of alleles in a particular gene pool remains constant over time
        • Equation = p2 + 2pq + q2 = 1
          • P = Dominant (AA)
          • Always equal to 1 (100%)
          • Q = Recessive (aa)
          • PQ = Aa
          • Allele Frequency Equation - Allele Count/Total number of alleles
          • Corrected allele frequency equation - Add 2 alleles onto the allele count and divide by new total of alleles used to construct database
            • Known as balding - 95% confidence interval to correct for sampling errors
          • Genotype proportion equation - Allele frequency at the 1st allele x allele frequency at the 2nd allele x 2 (2pq)
          • Profile Frequency - Times the genotype frequency at each locus (product rule)
      • Deviation from the Hardy Weinberg equilibrium
        • The HW law states that certain criteria must be met in order to estimate the allele and genotype frequency.
          • The population is free from effects of migration
          • Random mating occurs within the population
          • There is no natural selection
          • The population is indefinitely large
          • No mutations occur
          • It is clear that NO population will be able to meet all of these criteria's
            • if a population does meet this criteria, then it is said to be in Hardy-Weinberg Equilibrium
      • Based on the mendelian inheritance
        • Genes and traits that are passed from parent to child
      • Determine frequencies of genotypes
  • A population can be described as a group of people sharing common ancestry.
    • it is not possible to estimate allele frequencies from the whole population as this would require testing everybody
      • Population databases therefore represent a subset of the population

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