Uses of DNA Profiling Flashcards
Uses of DNA Profiling?
Forensic casework
Paternity
Identification- mass disasters, no ID on body
Genetic Diseases
What are the methods of DNA profiling?
RFLP (Restriction Fragment Length Polymorphisms)
PCR (polymerase chain reaction)->STRs (short tandem repeats)- amplifies specific sections of DNA (3-7 bases), more likely to get results especially with degraded samples
Low Copy Number
Familial Searching- similar profile on DNA database
Y-STR testing- targeting male cells, approx. 200 Y-STR sites on Y chromosome, problem- less variation meaning less discrimination between people
Mitochondrial DNA-link family members, hair sample with no root
DNA Boost- computer programme (2005) helps to separate mixed samples
What is the CODIS system used for?
Combined DNA index system (USA)
Use 13 core STR loci
What is the NDNAD used for?
National DNA Database UK
Use 10 STR loci and XY- X chromosome 6 bases shorter than Y chromosome (Amelogenin)
What is the percentage of the UK population with their DNA profile on the database?
5.2%
What is the percentage of the USA population with their DNA profile on the database?
0.5%
What do the labels above peaks represent?
The loci being looked ay
Why do peaks differ in size?
Number of bases present in DNA
What is the probability that someone would watch random DNA sample at any one site?
1/10
What is the probability that someone would watch random DNA sample at any three site?
1/1000
What is the probability that someone would watch random DNA sample at all 13 CODIS sites?
1 in ten trillion
How does site matching make the match likely to be reliable?
World population is 6 billion so very it can’t be anyone else if it’s one in ten trillion
Why do increased sites increase reliability?
Increased sites means less likely to match a sample at random
What does exclusion mean?
Non-match
What does inclusion mean?
Match
Why may there be inconclusive results?
May be due to analysis, quantity of DNA (difficult to get a full profile), difference in opinion between two analysts
How do you calculate the frequency of two allele locus?
Frequency of allele 1, f(1)=p
Frequency of allele 2 f(2)=pxp p2
When is low copy number used?
Very few cells, international cases
Skin sweat in fingerprints (few cells)
Why does LCN take longer?
Repeat more cycles because less DNA to start with, issues with sensitivities, may obtain DNA profile that’s not connected to the case
What are cold cases?
Cases open for a long time but are never solved
What is familial searching?
Have full DNA profile
No matches on DNA database
Similar DNA within family group
Alternatively- partial profile- try to match
What can particular markers indicate?
Ethnicity
What has DNA technology led to an increase of?
Examination of “Cold cases”
What are the issues to consider?
Contamination
Changes in guidelines- samples weren’t collected as efficiently as they are now
Continuity of evidence i.e. possibility of tampering from collection to storage
Storage of material e.g. microscope slides- may have badly degraded if not properly stored
