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2nd year sem 1: Forensic Genetics > Lecture 4: Population genetics > Flashcards

Lecture 4: Population genetics Flashcards

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1
Q

what advantages does a DNA database bring to criminal investigation?

A
  • criminals reoffended
  • severity of crimes done increase
  • small number of criminals can be responsible for a large number of crimes
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2
Q

what are the two sections of NDNAD?

A
  • profile generated from evidence collected from crime scenes ( full or partial)
  • full DNA generated from individuals.
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3
Q

what does a crime scene sample need to contain before it can be uploaded to the NDNAD?

A

minimum of 4 pairs of numbers and a sex marker

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4
Q

whats FINDS?

A

Forensic Information Database Service

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5
Q

what representatives sit on the FIND board?

A

– 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

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6
Q

The retention of DNA samples is controlled by who?

A

the Police and Criminal Evidence Act 1984

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7
Q

whats on the NDNAD legislation?

A
  • DNA destroyed after profile, destroyed within 6 months.
  • PACE not applied to volunteers missing persons references
  • criminal procedure investigations act regulate extension for casework.
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8
Q

Any age convicted for qualifying 2 offence, how long is DNA kept?

A

indefinite

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9
Q

Adult convicted of minor 3 offence, how long is DNA kept?

A

indefinite

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10
Q

under 18, minor, (give youth caution), of a mini offence, how long id DNA kept?

A

first offence: 5 years
indefinite, if prison sentence more than 5 years
2nd conviction: indeifnite

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11
Q

whats a speculative search?

A

If under the PoFA a subject profile cannot be retained, the act does allow for a search to be conducted against the NDNAD.

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12
Q

when can non routine searches be preformed?

A

performed on crime scene profiles that do not meet the loading requirements.

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13
Q

who developed familial searching?

A

FSS

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14
Q

when is familial searching used?

A

serious offences

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15
Q

In 2017/2018, how many familial searches were carried out?

A

13

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16
Q

when was familial searching first used, what was the case?

A

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.

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17
Q

Joseph James deAngelo was part of what case?

A

Golden State Killer case

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18
Q

When comparison of DNA profiles from evidence and reference samples fail to exclude an individual, what must happen?

A

statistics must be used to evaluate the significance of the match

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19
Q

what is population genetics?

A

Population genetics is the study of the causes of observed patterns of inherited genetic variation within populations

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20
Q

what is population genetics used for?

A

to apply a statistical significance to the value of a match between two DNA profiles

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21
Q

when is population genetics important?

A

when dealing with variability and uncertainty, especially in a court of law

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22
Q

it must be careful that the rarity of a profile is ___ over estimated

A

not

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23
Q

Statistical basis of the evidence is determined using what?

A

allele databases

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24
Q

what are the three ways a DNA match can be communicated?

A
  1. Combined Probability of Inclusion (CPI) or Exclusion (CPE)
  2. Random Match Probability (RMP)
  3. Likelihood Ratio (LR)
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25
Q

This separation of each pair of alleles is _______ from the separation of others

A

independent

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26
Q

what happening during meiosis produces variation?

A

crossing over

27
Q

____ _______ gives rise to the variation we see due to both independent assortment of alleles and recombination.

A

Genetic shuffling

28
Q

what does meiosis produce?

A

4 individual gametes

29
Q

meiosis quick steps

A

. DNA replicates – 2 chromatids

  1. Crossing over
  2. Meiosis I
  3. MeiosisII
  4. 4individualgametes
30
Q

whats the hardy weinberg principle?

A

within a randomly mating population the genotype frequencies at any one locus remain constant

31
Q

whats the HWE equation?

A

p2 + 2pq + q2 = 1

32
Q

what can be calculated form allele frequencies?

A

genotype frequencies

33
Q

what is probability?

A

Probability is the ratio of the number of actual occurrences of an event to the number of possible occurrences

34
Q

what are the 3 laws of probability?

A
  • Between 0 and 1
  • Events can be mutually exclusive
  • The probability of 2 independent events occurring simultaneously is the PRODUCT of their individual probabilities
35
Q

whats a population in statistical terms?

A

a set of objects of interest which is either infinite or so large as to be immeasurable in total

36
Q

what is a sample?

A

A sample is a subset of the population that can be measured, e.g. 200 UK males

37
Q

whats the statistic being examined ?

A

a genotype or allele

38
Q

whats needed to support DNA 17?

A

allele database

39
Q

How are Allelic databases constructed?

A

y measuring the frequency of occurrence of an allele within a population

40
Q

To create a Allelic databases how many people need to be sampled?

A

several hundred people, no relation, the larger the sample the more representative of the whole population

41
Q

allele databases are used to calculate the genotype frequencies but how?

A

using 2pq or p2

42
Q

The sum of all genotype frequencies should equal ?

A

1

43
Q

Homozygotes?

A

p2 or q2

44
Q

Heterozygotes?

A

2pq

45
Q

The STR alleles used in forensic investigation multiplexes are all inherited _____ of each other.

A

independently. (independence of loci)

46
Q

whats a syntenic STR pair?

A

Some STR loci are located on the same arm of a chromosome

47
Q

profile frequency can be calculated using what rule?

A

product rule

48
Q

how is product rule used to calculate profile frequency?

A

multiply genotype frequency at each locus, L1 x L2 etc

49
Q

whats the minimum quoted match probabiltiy?

A

1 in 1 billion’ as the minimum

50
Q

whats the maximum match probability retention value?

A

1 billin

51
Q

what needs to be considered when reporting match probability ?

A
  • allele from different population groups
    =allow for sampling effects
  • consider linkage between syntenic loci
  • good methods for the interpretation of mixtures
52
Q

How to test for HWEat a locus?

A
  • Compare observed and expected heterozygosities for that locus
53
Q

EH =?

A

1 - SUM(allele frequency data a^2+b^2….)

54
Q

OH=?

A

1 - SUM(homo genotype frequency data a,a + b,b + c,c……..)

55
Q

How can OH and EH be used to determine if the population can be said to be in HWE at a specific locus?

A

OH has to fall within 2 standard errors of EH to be in HWE

56
Q

what cognitions must be met for HWE?

A 
– Infinitely large population
– Random mating
– No migration
– No natural selection
– No mutation
57
Q

what are finite populations affected by?

A

random genetic drift

58
Q

sexual selection does not affect what?

A

STR loci

59
Q

whats it called when Migration can lead to changes in the gene pool?

A

Wahlund effect

60
Q

HWE is concerned with the ______ of alleles at one locus.

A

independence

61
Q

what can cause Linkage disequilibrium?

A

alleles that are physically close on a chromosome but also by population subdivision.

62
Q

Challenges to DNA evidence often focus on what?

A

inaccurate allele frequency databases which can lead to inaccurate profile frequencies being calculated

63
Q

what happens when there is a rare allele?

A

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.

2nd year sem 1: Forensic Genetics (8 decks)

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