DNA profiling

Question 1

Who discovered DNA profiling?

Answer 1

Sir Alex Jeffreys 1984

whilst looking at genetic variation in disease

Question 2

First use?

Answer 2

In the conviction of Colin Pitchfork 1987

Question 3

DNA sources

Answer 3

blood, bones, teeth, tissues, semen, urine, hair, saliva

Question 4

RFLP - Restriction Fragment Length Polymorphism

Answer 4

• uses restriction enzymes to cut DNA
• variable number of tandem repeats
• large amounts of DNA required
• requires undegraded material
• warm/moist conditions increase degradation

Question 5

PCR- Polymerase Chain Reaction

Answer 5

Short tandem repeats

• less DNA required
• can be partially degraded and still build profile
• limitations? - contamination

Question 6

PCR

Answer 6

• Used to make lots of copies of specific sections of DNA -STRs
• One cycle of PCR goes through a series of temp changes
• Amplifies DNA copies
• These copies then analysed using gel electrophoresis - separated according to size

Question 7

STR-Short tandem repeats

Answer 7

DNA has variety of STRs

• people vary in n.o. of repeats at STR loci
• Use PCR - recognise constant conserved sequences

Question 8

SNPs

Answer 8

• Single nucleotide polymorphisms

- differences in a single base unit

Question 9

Stutter bands

Answer 9

DNA repeats slipping out of register during PCR
Usually 1 repeat length smaller than the main band
mechanism= Deletion caused by forward slippage

Question 10

Partial profiles

Answer 10

• used for familial searching
• prioritise using specific parameters
• can use low copy number profiling

Question 11

LCN - low copy number

Answer 11

• copy 10 informative sites from smaller amount of starting material
• takes longer to process
• used in familial searching

Question 12

Mitochondrial DNA

Answer 12

• 1mitochondrion has 5-10 identical circular molecules of DNA
• each has 37 genes
• useful in mass disasters to link family members

Question 13

Y Chromosome STR testing

Answer 13

• amelogenin locus and/or

- STRs on Y chromosome

Question 14

% of population with their profile on the DNA database

Answer 14

UK-5.2%

USA -0.5%

Question 15

Probability that someone would match random DNA sample…

Answer 15

3 sites = 1/1000

13 (CODIS) = 1 in ten trillion

Question 16

Exlusion

Answer 16

non-match

Question 17

Inclusion

Answer 17

match

Question 18

Low Copy Number LCN

Answer 18

• very few cells
• international cases
• skin, sweat in fingerprints
• takes longer
• cold cases

Question 19

Familial searching

Answer 19

• full DNA profile
• no matches on DNA database
• similar DNA within family group

Question 20

M3 Murder (2003)

Answer 20

Craig harmen, DNA on brick

Question 21

Cold cases

Answer 21

DNA boost (Computer -based analysis system to interpret mixtures)

Question 22

Issues to consider

Answer 22

• contamination
• changes in guidelines
• continuity of evidence
• storage of material

Question 23

First use of Familial Search -cold case

Answer 23

Dec. 2001 -Joseph Kappen match for DNA found on profiles on cold murder case

Question 24

Paternity

Answer 24

child has two alleles
mitochondrial dna from mother
Y chromosome (if boy) from father

Question 25

Using DNA profiling for identification: Bosnia

Answer 25

Former Yugoslavia -est. 30/40,000 bodies

• blood and bone samples
• profiles of bodies compared with those of living relatives
• difficulties -a)whole families killed
  b) Bones scattered

Question 26

9/11 2001

Answer 26

• 3000 deaths
• new extraction methods from bone
• mini STRs
• SNPs
• Mt DNA

Question 27

Genetic diseases

Answer 27

• current standard forensic DNA tests do not look at genes
• mutations in genes can lead to defects
• denetic diversity–> polymorphism
• mutations within restriction sites changes the sizes of fragments
• detect genetic diseases by RFLP or PCR

Question 28

Modern use of Y-STR testing

Answer 28

Sadaam Hussein (confirmed his identity by matching Y-STR Halotype to sons)