Benefits of newer multiplexes Flashcards
1
Q
What are the combinations of loci called?
A
- Multiplex
- Multiplexing is a term that refers to multiple samples being processed at the same time, usually to save time and money.
- Multiplex PCR is a technique whereby PCR is used to amplify several different DNA sequences simultaneously.
2
Q
Second generation multiplex
SGM
A
When the National DNA Database was set up in 1995 the test used to produce DNA profiles what called SGM.
Second-Generation Multiplex
The test comprised of six loci
Plus, a test (AMEL) indicating the sex of the donor.
3
Q
Second generation multiplex
Mistaken identify
A
- April 1999, UK matched a burglary crime scene sample to a man on the DNA database (domestic violence).
- Six Loci match (one in 37 million)
- However they lived 200 miles away from burglary and had advanced Parkinson’s (could not drive)
- Additional testing at the request of the defence for additional loci excluded the individual.
4
Q
SGM+
A
- As the database grew larger it became clear that more discrimination was needed, and so new loci were included.
- In 1999 the test used to provide DNA profiles for the UK DNA database was upgraded.
- The number of loci increased to 10 and the name of this new multiplex of called SGM+
- This new test included all of the previous SGM loci plus the sex test so that the test was back-compatible with the previous SGM multiplex.
5
Q
Three types of DNA match
A
- Between a reference samples and undetected crimes.
- Crime to crime matches in order to provide an investigative link between the two and particularly helpful in undetected crimes.
- Person-to-person (between reference samples) which identifies duplicates were people have given different names.
6
Q
- DNA is a polymer made up from monomers called?
- This phosphate forms the backbone of the DNA strands
- The two DNA strands are held together by these bonds?
- The combination of DNA loci are referred to as a?
- The multiplex, used the formation of the DNA database, in 1995 was referred to as?
- DNA bases can be categorised as either purine or?
A
- DNA is a polymer made up from monomers called nucleotides.
- Sugar phosphate forms the backbone of the DNA strands.
- The two DNA strands are held together by hydrogen bonds.
- The combination of DNA loci are referred to as a multiplex.
- The multiplex, used the formation of the DNA database, in 1995 was referred to as SGM.
- DNA bases can be categorised as either purine or pyrimidine.
7
Q
So why DNA 17 & why now?
A
- The mounting number of requests from police and investigators for undetected DNA profiles to be searched against databases from other countries.
- The ease of travel between different countries gives more opportunities for those fleeing justice to escape abroad
- To deal with cross-border and inter-country crime.
8
Q
Samples profiled using different multiplexes
A
These are investigated using a near match report system.
* This lists one allele differences between profiles.
* It can also be extended to investigate two or three allele differences between reference samples if needed.
9
Q
Reasons for non-concordance between different multiplexes
A
- May be data entry error – the typing or writing of the incorrect number .
- Some will be because the two profiles are very similar.
- Mutation - This is where a crime stain is profiled using one multiplex might be an 18 – 18. The reference using a different multiplex might be 18 – 19.
- These can be investigated by retesting the crime stain and the reference sample using the other multiplex.
10
Q
Prum convention 2005
A
Many EU countries signed up enabling the routine exchange of data of:
* DNA profiles
* Fingerprints
11
Q
European standard set (ESS)
A
- Sets of seven loci were specified as the basic set for comparison.
- These were called European Standard Set or ESS of loci.
- At least six of the ESS loci are needed before a search can be carried out.
12
Q
DNA 17 - Internation perspective
A
- As the size of the databases grew and the number of searches increased it became clear that there were some problems due to the small number of loci which are common between the profiles been searched across different databases.
- There were more false positives or advantageous matches that needed further testing.
- Additional DNA testing of most loci is needed to investigate these matches so than further tests on both samples must be commissioned from one or both the countries involved.
- These false positive matches are mostly seen where the number of loci that can be compared is limited.
- It is obvious that one way of cutting this requirement for further work is to add more loci to the standard test.
13
Q
- Quite apart from the benefits of international searching, there were two other improvements delivered by DNA 17. One reduced the possibility of adventitious matches, and the other benefit, ability to deal with this type of DNA sample?
- In instances where a crime stain is profile using one multiplex and a reference sample uses a different one then the resulting comparison may not match for a variety of reasons. In this instance, it is said to be?
- The European standard set, specified how many loci as the basic set for comparison
- Many EU countries signed up to this convention enabling the routine exchange of DNA data, in 2005?
- How many ESS Lucite are needed to be identified before an international search can be carried out?
- There are several reasons for non-concordance. For example, this may be due to a data entry error or sometimes the profiles can be very similar. What is another reason for non-concordance?
A
- Quite apart from the benefits of international searching, there were two other improvements delivered by DNA 17. One reduced the possibility of adventitious matches, and the other benefit was the ability to deal with a degraded DNA sample.
- In instances where a crime stain is profile using one multiplex and a reference sample uses a different one then the resulting comparison may not match for a variety of reasons. In this instance, it is said to be non-concordant.
- The European standard set, specified 7 loci as the basic set for comparison.
- Many EU countries signed up to the Prum convention enabling the routine exchange of DNA data, in 2005?
- Six ESS Lucite are needed to be identified before an international search can be carried out?
- There are several reasons for non-concordance. For example, this may be due to a data entry error or sometimes the profiles can be very similar. The other reason for non-concordance is mutation.
14
Q
Sample quality
In crime stains
A
Also, the profiles obtained from crime stains were often too poor to be searched at all because the DNA was damaged
- Either because it was breaking down or degraded.
- Or because of the presence of chemicals in the sample which inhibited the DNA reaction.
15
Q
European network of forensic science (ENFSCI)
Improved DNA test
A
- The European Network of Forensic Science Institutes put forward an agreed set of requirements for an improved DNA test.
- Then manufacturers develop their own competing systems to at least meet these requirements. The requirements were to include more loci, to be more robust to inhibition and to get better results from smaller and more degraded samples.
- More systems meeting these requirements are becoming available all the time. 17 loci were specified in the requirement and the test is referred to as DNA 17.
