# DNA Profile Interpretation

• 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