Topic 5 - Single Source Interpretation

Question 1

is a single sourced DNA profiles common or rare

Answer 1

rare

Question 2

what is the chance of a coincidental match of a single source profile

Answer 2

very small

Question 3

what 3 things can the value of the statistics of random match probabilities be reduced by

Answer 3

mixtures

incomplete profiles

relatives

Question 4

would you expect to see a mixture in a reference sample

Answer 4

no

Question 5

what is the overall question addressed when interpreting a complete single source profile

Answer 5

what is the chance that a randomly chosen, unrelated person would have the same DNA profile that we are seeing in the evidence sample

Question 5

what must accompany a DNA profile in an expert witness report

Answer 5

a statistic - giving the profile a weight giving its value as evidence

Question 6

where is it common to see mixtures in DNA profiles

Answer 6

in crime scene samples

Question 7

what do the numbers represent for the alleles

Answer 7

the number of base pair repeats at the particular loci

Question 8

what are the two things we do when comparing DNA profiles

Answer 8

see who can be a contributor and who can be excluded

using the reference samples

Question 9

when can we exclude a reference sample from being a match to a DNA profile

Answer 9

when one or more alleles fail to match at any of the loci

Question 10

when can we say a reference sample is a possible contributor to a DNA profile

Answer 10

when all alleles in the reference are also found in the scene sample all the loci

Question 10

when do we not have to add a statistical attachment to a conclusion

Answer 10

when a sample is excluded as being a match

Question 11

how is the weight of a DNA profile match assessed

Answer 11

using a statistical analysis

Question 12

how can DNA evidence lead to wrongful convictions

Answer 12

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

Question 13

when calculating loci frequencies what do we use

what does this calculation performed depend on

Answer 13

the product rule

if the loci is homozygous (alleles are the same) or heterozygous (alleles are different)

Question 14

what is an underlying assumption made when we apply the product rule in calculating loci frequencies

Answer 14

1. alleles inherited are done so independently within a locus and across loci - if this isn’t true we cant apply the product rule

Question 15

what principle forms the product rule used to calculate loci frequencies

Answer 15

the Hardy Weinberg principle

P^2 + 2PQ + Q^2 = 1

where P^2 is the freq of homozygous and 2PQ is freq of heterozygous

Question 16

what calculation is done to find the loci freq of a heterozygous locus

Answer 16

2PQ where P and Q are the allele frequencies in a given population found at the locus

Question 17

what calculation is done to find the loci freq of a homozygous locus

Answer 17

P^2 where p is the allele freq in a given population of the allele at the locus

Question 18

what is calculated after the loci frequency

how is this done

Answer 18

the profile frequency

done by multiplying all loci frequencies together

Question 19

what type of databases are used to get allele frequency data

Answer 19

allele frequency reference databases

divides into different populations e.g Caucasian

can use the national DNA database to create this database

Question 20

how do we get from profile frequency to random match probability

how is this written

Answer 20

1 divided by profile frequency

represented as 1 in the number

Question 21

when is random match probability calcualted

Answer 21

when we have single source, unmixed profiles