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DNA > Topic 1 - DNA > Flashcards

Topic 1 - DNA Flashcards

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1
Q

give two samples that fluoresce when observed under UV light

A

saliva and semen

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2
Q

what does the detection of semen rely on the presence of and what can this sometimes lead to

A

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

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3
Q

what is the name of the presumptive test for semen and what is this generally followed up by

A

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

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4
Q

how are blood samples being used for DNA analysis stored

A

in vails containing EDTA to preserve them

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5
Q

why is semen a better DNA source than blood

A

Semen is purely DNA whereas blood has many other components

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6
Q

what two categories can human blood cells be split into and give an example of each

A

those with a nucleolus = leucocytes or white blood cells

those without = red blood cells or platelets

red blood cells make up45% and white 1%

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7
Q

can DNA be extracted from urine and faeces

A

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

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8
Q

what are the two outcomes form a presumptive test and what do these mean

A

positive = a presumption = continue with further testing

negative = a rejection = cease analysis

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9
Q

name three presumptive tests for blood

A

luminol
KM (kastle mayer)
LMG - luminol

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10
Q

what are the two presumptive tests for saliva

A

ELISA test = enzyme linked immunosorbent test
phadebas test = use blotting paper and weigh it down over sample - blue is a positive result

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11
Q

what is another purpose of the ELIZA test other than saliva

A

drug screening - testing for the presence of drugs

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12
Q

what are the main differences between DNA and RNA (5)

A
  1. RNA = single stranded, DNA is double
  2. RNA has a ribose sugar DNA has deoxyribose
  3. RNA has Uracil rather than Thymine
  4. DNA stores genetic info, RNA involved in protein synthesis
  5. DNA found in nucleus RNA in nucleus and cytoplasm
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13
Q

what was DNA fingerprinting and when was it invested

A

a technique used to distinguish between individuals of the same species using their DNA

invested in 1985 by Sir Alec Jeffreys

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14
Q

what was the technique developed after DNA fingerprinting

briefly explain what this is

A

DNA profiling also known as DNA typing

a method of looking at the DNA characteristics of an individual

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15
Q

what are the 4 main steps in DNA profiling

A
  1. extraction and purification
  2. quantification
  3. PCR for amplification
  4. electrophoresis for separation and STR analysis
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16
Q

what is DNA extraction and what are the three steps involved in this

A

removing DNA from the nucleus of cells in the sample and purifying it

  1. lysis = break open cell
  2. precipitation = use of metal ions to neutralise the DNA and adding alcohol to precipitate the DNA
  3. purification = wash the precipitate away with alcohol
17
Q

what is the purpose of PCR

A

to quickly make millions of copies of the DNA sample so it can be used for analysis

18
Q

what are STR regions and why are they used in forensic DNA analysis

A

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

19
Q

what problem do twins possess in DNA analysis

A

identical twins have identical genetic information so their STR profiles will match

so we can differentiate between these individuals looking at fingerprints

20
Q

what is the purpose of electrophoresis

A

separating DNA fragments by their size

21
Q

what does a DNA profile show

A

a distinctive pattern of a persons DNA that has been separated in electrophoresis

22
Q

what would deem two DNA profiles a match

A

if all the bands on the DNA profile are in the same place

23
Q

what are two uses of DNA profiling

A

paternity testing
forensic investigation

24
Q

what is produced in electrophoresis

A

an electropherogram = a graph showing the alleles found at each locus analysed

25
Q

what are the two types of DNA that can be used in DNA profiling

A

mitochondrial DNA
nucleic DNA

26
Q

what is meant by the term polymorphic

A

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

27
Q

what does analysing a greater number of loci allow for

A

better discrimination and less likely the chance of randomly obtaining the same profile for two different sample

27
Q

why is quantification part of the DNA profiling process

and what technique is normally used for this

A

this allows us to optimise the number of PCR cycles depending on how much of the sample we have

using qPCR

28
Q

what are the two types of electrophoresis and what is the most commonly used now

A

gel and capillary

capillary is more used now

29
Q

what is the supernatant and at what stage is it formed in DNA analysis

A

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

30
Q

what are the two main types of peaks seen in electropherograms and what do these mean

A

homozygous peak = the same allele is inherited from both

heterozygous peaks = two different alleles inherited from both parents

31
Q

what suggest the presence of a complete single source DNA profile

A

one or two allele peaks at each loci

32
Q

what is the distinguishing feature between a homozygous and a heterozygous peak in a single source profile

A

homozygous will be double the height of a heterozygous

33
Q

what are the two main issues that result in difficulty in interpreting DNA profiles

A

the presence of a mixture (multiple DNA sample)

degraded DNA

33
Q

what do we call the smaller peaks next to the allele peaks in a DNA profile

A

artefacts or noise

34
Q

what is the thing that flaws DNA analysis making it unable to make activity level propositions

A

the ease of DNA transfer - the fact this can be secondary and tertiary and persists well

34
Q

what level proposition is a DNA profile match

A

source level

35
Q

what is the case that was used to argue that the use of DNA evidence is flawed

A

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

DNA (16 decks)

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