Topic 4 - Modern DNA Multiplexes Flashcards
what are the combinations of loci looked at in DNA analyses called
multiplexes
what is ESS
the European standard set = the standard loci for DNA analysis
includes 7 loci specified to be included to make comparisons between profiles
6 loci are needed to perform an international search
what was SGM
the test that was being used when the National DNA database was set up in 1995
second generation multiplex
using 6 loci plus AMEL indicating the sex
why was a new multiplex system (improving on SGM) needed
in 1999 a match was found on the database but the person was very unlikely to have committed the crime = adventitious match
the need for a more discriminative method was needed
what are the three types of DNA match observed in forensic DNA analysis
- reference samples and unknown crimes
- crime to crime = giving investigative links
- person to person = between references and samples, can be used to identify duplicates if someone has given a false name
what was the next multiplex developed after SGM
SGM+
this built on the 6 loci used in SGM - 10 loci were now included
give three things DNA profiling can be used for
- paternity testing
- crime scene investigation
- DVI - disaster victim identification
if a samples DNA profile can not be found on the database what is done next to give an investigative lead
a familial search to see if any of these may be on the database
why was DNA 17 developed (2)
SGM+ was working well but there was still the need for more discrimination so this multiplex was introduced using 17 loci- there were adventitious matches still occurring
SGM+ also struggled with degraded DNA = not very sensitive
why do police officers often as for DNA profile searches against databases from other countries (2)
give some examples of crimes this search is often related to (4)
- to prevent criminals fleeing justice by moving abroad
- deal with cross-border and inter-country crime
terrorism
trafficking
drug smuggling
DVI
what must be used in order to make comparisons between reference and crime samples
the same profiling and multiplex system
what is near match reporting
when is it applied
what can this suggest
when a crime scene sample and reference sample do not exactly match but have enough allele matches to be considered potentially relevant
applied when there is 1-3 allele difference
this could suggest the actual match is a relative of the individual giving the reference sample
give 4 suggestions as to why the allele difference may be seen in near matches (non-concordance)
how are these issues overcome
- data entry errors (prevented by using automated computer systems)
- primer binding site mutation
- use of two different multiplex instruments
- two very similar profiles - so confusion
overcome by retesting the crime scene samples and reference ensuring the same multiplex is used
what was the Prum Convention in 2005
did the UK accept this idea
the routine exchanging of data from DNA and fingerprint databases across countries in the EU
no, many different countries use different multiplex systems so shouldn’t really be compared
what is ENFSI and
what did they do about DNA analysis
the European Network of Forensic Science
agreed set requirements for an improved DNA test
- include more loci (17)
- be more robust to inhibition
- get better results from smaller and/or degraded samples
what 2 things were commonly found leading to poor crime samples so DNA profiles could not always be found
- degraded DNA
- things in the samples that would inhibit elements of the profiling process
what makes comparing across different multiplexes difficult
the order and position of the loci are not the same between different multiplexes = room for more error in comparisons by eye
what does allow continuity and back compatibility between new and old DNA multiplex systems
the original 6 loci in SGM was included in SGM+ and the 10 here were included in DNA 17
give three benefits of DNA 17 over SGM+
more discriminative = uses 17 loci
more sensitive = starting threshold of 500pg (more than half of threshold in SGM+) sensitivity has doubled
less effect by inhibition by soil, microbes, plant and faecal contamination
how has DNA 17 affected the PCR process
lower amounts and degraded DNA can be analysed so the number of PCR cycles has increases from 28 to 29-31
what is a problem with the fact that DNA 17 has an increased sensitivity
contamination will have a greater affect and even slight contamination may impact the profile
how many loci does the multiplex that Scotland uses have
one that looks at 21 loci
