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DNA > Topic 3 - How to Generate Profiles ' > Flashcards

Topic 3 - How to Generate Profiles ' Flashcards

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1
Q

before DNA 17 what were the three types of test used to generate DNA profiles in order of invention

A

RFLP
DQ Alpha
Automated STR

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2
Q

what does RFLP stand for

when were these tests used

A

restriction fragment length polymorphism

used in the 80s and 90s

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3
Q

how long did RFLP take to generate a profile

A

one month or more

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4
Q

what were the profiles generated by RFLP called

A

auto-radiographs

these resembled an X-Ray plate and look like bar code patterns

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5
Q

what was good about RFLP

A

it was very discriminating

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5
Q

what was the name of the case that first used DNA in the conviction

A

Colin Pitchfork

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5
Q

in DQ alpha, what showed us the DNA molecules in the sample

A

the presence and absence of blue dots on test strips

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6
Q

what was DQ Alpha the first type of

what was this also called

A

DNA profiling method based on PCR

also called poly-marker

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6
Q

what were the 2 benefits of DQ Alpha over RFLP

A

could work with much smaller samples (more sensitive)

results generated quicker - in half a day rather than a month or more

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7
Q

what are known as the genetic scissors

A

restriction enzymes

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8
Q

what is meant by discrimination power

A

the ability to differentiate between two things

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9
Q

what is meant by an advantacious match

A

a random match that occurred by chance due to using a low number of loci

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10
Q

in 1985 what was the name of the DNA profiling method used by Sir Alec Jeffrey

what were the 3 things wrong with this method

A

MLP = multi locus probe

lengthy, needed a lot of sample, results were complex

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11
Q

in 1987 what was the process called that was used in DNA profiling

how was this an improvement from MLP (2)

what was still lacking with this method (3)

A

Single Locus Probe (SLP) or VNTR = variable number tandem repeats

easier to interpret results, quicker

lacked sensitivity, poor results with degraded samples, difficult to resolve mixtures

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12
Q

how many controls were run in SLP

A

2

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12
Q

did RFLP or DQ Alphas have higher discriminative value

A

RFLP

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13
Q

what match probabilities could be assigned with

a) RFLP
b) DQ Alpha

A

a) 1 in 1 million
b) 1 in a few hundred or few thousand

DQ Alphas was less discriminative but more sensitive

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14
Q

what is meant by sensitivity

A

the amount of starting material or the size of the stain that can be worked with

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14
Q

what is meant by automated STR profiling and why was this beneficial

A

the use of automated systems to analyse the STR regions in DNA samples

increased efficiency, accuracy and throughput of DNA samples. also higher discriminative power and sensitivity

14
Q

what are the 6 criteria used to assess whether a profiling method is good or not

A

discriminating power
sensitivity
ability to deal with artefacts
speed
ability to deal with mixtures
ability to conduct a database search

15
Q

is analysis using mitochondrial DNA or automated STRs more sensitive and why

A

using mitochondrial DNA is more sensitive because each cell contains the genetic material

but each cell also has thousands of mitochondria and each of these have copies of mitochondrial DNA

16
Q

what is the volume range we typically deal with in DNA analysis

A

10-20 microlitre

using micropipettes

16
Q

what can be used in electrophoresis to reduce the human interaction with samples

A

an autosampler

16
Q

what is the type of profiling that focuses on DNA that is paternally inherited

briefly explain this method

A

Y-STR profiling

STR markers that reside on the human Y chromosome are considered

Y chromosomes are paternally inherited so male relative are likely to have the same = less discriminative

16
Q

what are the two downfalls of using mitochondrial DNA rather than nucleic DNA

A

mitochondrial DNA is only inherited from the mother - making it less discriminative as many maternal relative are likely to share this genetic material

this type of DNA can be small compared to nucleic DNA so less info is contained within it

16
Q

everyone has the same mitochondrial DNA as their…

A

mother

16
Q

when is Y-STR testing beneficial

A

when you have a mixed profile with a male and female contributor and you want to focus on the male profile

e.g sexual offence cases

16
Q

what is an allele

A

a region of DNA that varies between people - different forms of the same gene

two alleles are seen at each loci
one allele inherited from each parent

16
Q

how much DNA is recommended for the new DNA 17 multiplex

what does this mean about this method compared to previous ones

A

200-500 pg - cant be seen with the naked eye

more sensitive

16
Q

what amount of DNA do previous profiling kits recommend using

A

500-1000 picograms

100-200 cells

16
Q

what is meant by a polymorphism

A

regions of DNA that differ between individuals

16
Q

what are the regions of DNA that can be the same between individuals

A

coding regions - these code for things like eye colour or hair colour

not good to be used in profiling

16
Q

what is a
a) loci
b) locus

A

a) multiple locus
b) a specific location on a chromosome

16
Q

what are amplified fragments of DNA called

A

amplicons

17
Q

what is the purpose of the elution buffer in DNA extraction and purification

A

to remove the DNA bound to the silica column by breaking the hydrogen bonds

18
Q

in electrophoresis how are the DNA fragments measured

A

in RFUs - relative fluorescent units

a measure of light intensity picked up by a camera in the detector at different points in time

19
Q

what are the first peaks typically seen in PCR - these peaks look much larger than the amplified DNA peaks

A

primer residue

20
Q

how many coloured fluorescent markers are typically used in electrophoresis

A

4-6 - this is dependent on the type of multiplex being used

21
Q

how many peaks in an electropherogram signify a mixed profile

A

three or more peaks at any loci

22
Q

where are allele drop out peaks normally seen if they are present

A

the end of the EPG where the bigger fragments are as these are more susceptible to degradation

23
Q

which loci represents the biological gender of the sample

A

amelogenin

24
Q

what does the height of an allele peak represent

A

the relative amount of the allele

25
Q

are smaller or larger DNA fragments on the left side of the EPG

A

smaller

26
Q

what can we learn from an EPG (5)

A

biological gender

DNA profile - alleles present at each loci (homozygous or heterozygous)

single source or mixture

degraded sample - larger fragment allele peaks may be missing

peak height = relative amount of DNA

27
Q

what is SGM+

A

previously used automated STR multiplex looking at 10 loci

28
Q

what are the 5 hypotheses that could be put forward for observing a DNA match

A

same source

coincidence

contamination

analysis error or error in handling after collection

a mistake - could be deliberate or accidental

28
Q

how is the chance of an accidental match ruled out

A

with the use of statistics giving random match probabilities

DNA (16 decks)

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