Lecture 4: Population genetics Flashcards
what advantages does a DNA database bring to criminal investigation?
- criminals reoffended
- severity of crimes done increase
- small number of criminals can be responsible for a large number of crimes
what are the two sections of NDNAD?
- profile generated from evidence collected from crime scenes ( full or partial)
- full DNA generated from individuals.
what does a crime scene sample need to contain before it can be uploaded to the NDNAD?
minimum of 4 pairs of numbers and a sex marker
whats FINDS?
Forensic Information Database Service
what representatives sit on the FIND board?
– National Police Chiefs’ Council (NPCC)
– Home Office who run the NDNAD
– Association of Police and Crime Commissioners (APCC)
– the Chair of the Biometrics and Forensics Ethics Group
– theInformationCommissioner(orrepresentative)
– the Forensic Science Regulator (or representative) (FSR)
– the Biometrics Commissioner (or representative)
– representatives from the police and devolved administrations of Scotland and Northern Ireland
The retention of DNA samples is controlled by who?
the Police and Criminal Evidence Act 1984
whats on the NDNAD legislation?
- DNA destroyed after profile, destroyed within 6 months.
- PACE not applied to volunteers missing persons references
- criminal procedure investigations act regulate extension for casework.
Any age convicted for qualifying 2 offence, how long is DNA kept?
indefinite
Adult convicted of minor 3 offence, how long is DNA kept?
indefinite
under 18, minor, (give youth caution), of a mini offence, how long id DNA kept?
first offence: 5 years
indefinite, if prison sentence more than 5 years
2nd conviction: indeifnite
whats a speculative search?
If under the PoFA a subject profile cannot be retained, the act does allow for a search to be conducted against the NDNAD.
when can non routine searches be preformed?
performed on crime scene profiles that do not meet the loading requirements.
who developed familial searching?
FSS
when is familial searching used?
serious offences
In 2017/2018, how many familial searches were carried out?
13
when was familial searching first used, what was the case?
First used in 2003 with the conviction of Craig Harman for manslaughter after throwing a brick off a bridge which hit a lorry killing the driver.
Joseph James deAngelo was part of what case?
Golden State Killer case
When comparison of DNA profiles from evidence and reference samples fail to exclude an individual, what must happen?
statistics must be used to evaluate the significance of the match
what is population genetics?
Population genetics is the study of the causes of observed patterns of inherited genetic variation within populations
what is population genetics used for?
to apply a statistical significance to the value of a match between two DNA profiles
when is population genetics important?
when dealing with variability and uncertainty, especially in a court of law
it must be careful that the rarity of a profile is ___ over estimated
not
Statistical basis of the evidence is determined using what?
allele databases
what are the three ways a DNA match can be communicated?
- Combined Probability of Inclusion (CPI) or Exclusion (CPE)
- Random Match Probability (RMP)
- Likelihood Ratio (LR)
This separation of each pair of alleles is _______ from the separation of others
independent
what happening during meiosis produces variation?
crossing over
____ _______ gives rise to the variation we see due to both independent assortment of alleles and recombination.
Genetic shuffling
what does meiosis produce?
4 individual gametes
meiosis quick steps
. DNA replicates – 2 chromatids
- Crossing over
- Meiosis I
- MeiosisII
- 4individualgametes
whats the hardy weinberg principle?
within a randomly mating population the genotype frequencies at any one locus remain constant
whats the HWE equation?
p2 + 2pq + q2 = 1
what can be calculated form allele frequencies?
genotype frequencies
what is probability?
Probability is the ratio of the number of actual occurrences of an event to the number of possible occurrences
what are the 3 laws of probability?
- Between 0 and 1
- Events can be mutually exclusive
- The probability of 2 independent events occurring simultaneously is the PRODUCT of their individual probabilities
whats a population in statistical terms?
a set of objects of interest which is either infinite or so large as to be immeasurable in total
what is a sample?
A sample is a subset of the population that can be measured, e.g. 200 UK males
whats the statistic being examined ?
a genotype or allele
whats needed to support DNA 17?
allele database
How are Allelic databases constructed?
y measuring the frequency of occurrence of an allele within a population
To create a Allelic databases how many people need to be sampled?
several hundred people, no relation, the larger the sample the more representative of the whole population
allele databases are used to calculate the genotype frequencies but how?
using 2pq or p2
The sum of all genotype frequencies should equal ?
1
Homozygotes?
p2 or q2
Heterozygotes?
2pq
The STR alleles used in forensic investigation multiplexes are all inherited _____ of each other.
independently. (independence of loci)
whats a syntenic STR pair?
Some STR loci are located on the same arm of a chromosome
profile frequency can be calculated using what rule?
product rule
how is product rule used to calculate profile frequency?
multiply genotype frequency at each locus, L1 x L2 etc
whats the minimum quoted match probabiltiy?
1 in 1 billion’ as the minimum
whats the maximum match probability retention value?
1 billin
what needs to be considered when reporting match probability ?
- allele from different population groups
=allow for sampling effects - consider linkage between syntenic loci
- good methods for the interpretation of mixtures
How to test for HWEat a locus?
- Compare observed and expected heterozygosities for that locus
EH =?
1 - SUM(allele frequency data a^2+b^2….)
OH=?
1 - SUM(homo genotype frequency data a,a + b,b + c,c……..)
How can OH and EH be used to determine if the population can be said to be in HWE at a specific locus?
OH has to fall within 2 standard errors of EH to be in HWE
what cognitions must be met for HWE?
– Infinitely large population – Random mating – No migration – No natural selection – No mutation
what are finite populations affected by?
random genetic drift
sexual selection does not affect what?
STR loci
whats it called when Migration can lead to changes in the gene pool?
Wahlund effect
HWE is concerned with the ______ of alleles at one locus.
independence
what can cause Linkage disequilibrium?
alleles that are physically close on a chromosome but also by population subdivision.
Challenges to DNA evidence often focus on what?
inaccurate allele frequency databases which can lead to inaccurate profile frequencies being calculated
what happens when there is a rare allele?
To deal with rare alleles not found in databases, is set minimum frequency of 0.01 (1%), or 5/2N.
frequency less than this will be adjusted to avoid
under-representation within the database.
