Topic 1 - DNA Flashcards
give two samples that fluoresce when observed under UV light
saliva and semen
what does the detection of semen rely on the presence of and what can this sometimes lead to
relies on detecting the enzyme acid phosphatase
but this is a common enzyme so can lead to false positives e.g from onion skin or tea bags
what is the name of the presumptive test for semen and what is this generally followed up by
the AP (acid phosphatase test) = a sheet of blotting paper put over garment and spray AP over it - a blue colour is a positive result
followed up by DNA analysis
how are blood samples being used for DNA analysis stored
in vails containing EDTA to preserve them
why is semen a better DNA source than blood
Semen is purely DNA whereas blood has many other components
what two categories can human blood cells be split into and give an example of each
those with a nucleolus = leucocytes or white blood cells
those without = red blood cells or platelets
red blood cells make up45% and white 1%
can DNA be extracted from urine and faeces
the recovery of DNA here was hard as it inhibited components of the SGM test
DNA 17 is showing more promising results
mitochondrial DNA was more closely looked at previously but new multiplexes are better at extracting the DNA
what are the two outcomes form a presumptive test and what do these mean
positive = a presumption = continue with further testing
negative = a rejection = cease analysis
name three presumptive tests for blood
luminol
KM (kastle mayer)
LMG - luminol
what are the two presumptive tests for saliva
ELISA test = enzyme linked immunosorbent test
phadebas test = use blotting paper and weigh it down over sample - blue is a positive result
what is another purpose of the ELIZA test other than saliva
drug screening - testing for the presence of drugs
what are the main differences between DNA and RNA (5)
- RNA = single stranded, DNA is double
- RNA has a ribose sugar DNA has deoxyribose
- RNA has Uracil rather than Thymine
- DNA stores genetic info, RNA involved in protein synthesis
- DNA found in nucleus RNA in nucleus and cytoplasm
what was DNA fingerprinting and when was it invested
a technique used to distinguish between individuals of the same species using their DNA
invested in 1985 by Sir Alec Jeffreys
what was the technique developed after DNA fingerprinting
briefly explain what this is
DNA profiling also known as DNA typing
a method of looking at the DNA characteristics of an individual
what are the 4 main steps in DNA profiling
- extraction and purification
- quantification
- PCR for amplification
- electrophoresis for separation and STR analysis
what is DNA extraction and what are the three steps involved in this
removing DNA from the nucleus of cells in the sample and purifying it
- lysis = break open cell
- precipitation = use of metal ions to neutralise the DNA and adding alcohol to precipitate the DNA
- purification = wash the precipitate away with alcohol
what is the purpose of PCR
to quickly make millions of copies of the DNA sample so it can be used for analysis
what are STR regions and why are they used in forensic DNA analysis
STR = short tandem repeats
also known as non coding regions
they are an area of DNA that has a repeating base sequence
they are used as they are highly variable between individuals and looking at many different loci can give a characteristic profile of a person
what problem do twins possess in DNA analysis
identical twins have identical genetic information so their STR profiles will match
so we can differentiate between these individuals looking at fingerprints
what is the purpose of electrophoresis
separating DNA fragments by their size
what does a DNA profile show
a distinctive pattern of a persons DNA that has been separated in electrophoresis
what would deem two DNA profiles a match
if all the bands on the DNA profile are in the same place
what are two uses of DNA profiling
paternity testing
forensic investigation
what is produced in electrophoresis
an electropherogram = a graph showing the alleles found at each locus analysed
what are the two types of DNA that can be used in DNA profiling
mitochondrial DNA
nucleic DNA
what is meant by the term polymorphic
many forms, these regions have lots of variation in the population so we are less likely to randomly select two people with the same polymorphic regions
what does analysing a greater number of loci allow for
better discrimination and less likely the chance of randomly obtaining the same profile for two different sample
why is quantification part of the DNA profiling process
and what technique is normally used for this
this allows us to optimise the number of PCR cycles depending on how much of the sample we have
using qPCR
what are the two types of electrophoresis and what is the most commonly used now
gel and capillary
capillary is more used now
what is the supernatant and at what stage is it formed in DNA analysis
in DNA extraction after the cell lysis has occurred the sample is centrifuged
in this the cellular components other than the DNA create a pellet at the bottom of the tube and the liquid layer above this contains the DNA sample and is called the supernatant
what are the two main types of peaks seen in electropherograms and what do these mean
homozygous peak = the same allele is inherited from both
heterozygous peaks = two different alleles inherited from both parents
what suggest the presence of a complete single source DNA profile
one or two allele peaks at each loci
what is the distinguishing feature between a homozygous and a heterozygous peak in a single source profile
homozygous will be double the height of a heterozygous
what are the two main issues that result in difficulty in interpreting DNA profiles
the presence of a mixture (multiple DNA sample)
degraded DNA
what do we call the smaller peaks next to the allele peaks in a DNA profile
artefacts or noise
what is the thing that flaws DNA analysis making it unable to make activity level propositions
the ease of DNA transfer - the fact this can be secondary and tertiary and persists well
what level proposition is a DNA profile match
source level
what is the case that was used to argue that the use of DNA evidence is flawed
R vs David Butler
- he was a taxi driver charged with the homicide of a woman
due to DNA recovered from under her fingernails
-was found that the DNA was there due to a secondary contact
