Topic 5 - Single Source Interpretation Flashcards
is a single sourced DNA profiles common or rare
rare
what is the chance of a coincidental match of a single source profile
very small
what 3 things can the value of the statistics of random match probabilities be reduced by
mixtures
incomplete profiles
relatives
would you expect to see a mixture in a reference sample
no
what is the overall question addressed when interpreting a complete single source profile
what is the chance that a randomly chosen, unrelated person would have the same DNA profile that we are seeing in the evidence sample
what must accompany a DNA profile in an expert witness report
a statistic - giving the profile a weight giving its value as evidence
where is it common to see mixtures in DNA profiles
in crime scene samples
what do the numbers represent for the alleles
the number of base pair repeats at the particular loci
what are the two things we do when comparing DNA profiles
see who can be a contributor and who can be excluded
using the reference samples
when can we exclude a reference sample from being a match to a DNA profile
when one or more alleles fail to match at any of the loci
when can we say a reference sample is a possible contributor to a DNA profile
when all alleles in the reference are also found in the scene sample all the loci
when do we not have to add a statistical attachment to a conclusion
when a sample is excluded as being a match
how is the weight of a DNA profile match assessed
using a statistical analysis
how can DNA evidence lead to wrongful convictions
DNA is transferred very easily and persists well so may be found where the individual the profile belongs to hasn’t been
DNA should be supported by other evidence types not solely relied on
when calculating loci frequencies what do we use
what does this calculation performed depend on
the product rule
if the loci is homozygous (alleles are the same) or heterozygous (alleles are different)
what is an underlying assumption made when we apply the product rule in calculating loci frequencies
- alleles inherited are done so independently within a locus and across loci - if this isn’t true we cant apply the product rule
what principle forms the product rule used to calculate loci frequencies
the Hardy Weinberg principle
P^2 + 2PQ + Q^2 = 1
where P^2 is the freq of homozygous and 2PQ is freq of heterozygous
what calculation is done to find the loci freq of a heterozygous locus
2PQ where P and Q are the allele frequencies in a given population found at the locus
what calculation is done to find the loci freq of a homozygous locus
P^2 where p is the allele freq in a given population of the allele at the locus
what is calculated after the loci frequency
how is this done
the profile frequency
done by multiplying all loci frequencies together
what type of databases are used to get allele frequency data
allele frequency reference databases
divides into different populations e.g Caucasian
can use the national DNA database to create this database
how do we get from profile frequency to random match probability
how is this written
1 divided by profile frequency
represented as 1 in the number
when is random match probability calcualted
when we have single source, unmixed profiles
