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forensic science > DNA > Flashcards

DNA Flashcards

(39 cards)

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1
Q

name the four base pairs

A

adenine, thymine, cytosine, guanine

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2
Q

which two base pairs are purine

A

adenine and guanine

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3
Q

which two base pairs are pyrimidine

A

thymine and cytosine

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4
Q

what direction do DNA strands duplicate in

A

5’ to 3’

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5
Q

approximately how many base pairs are their in the human genome

A

3,000,000,000

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6
Q

how much of the human genome is coding DNA

A

less than 2%

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7
Q

which two areas of the cell contain DNA

A

the nucleus and mitochondria

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8
Q

where is nuclear DNA located

A

on the chromosome

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9
Q

which type of DNA contains STR’s

A

nuclear

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10
Q

which type of DNA lasts longer and why

A

mitochondrial as there is more of it in a cell

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11
Q

what can each somatic cell contain in humans

A

22 pairs of autosomal chromosomes and 2 sex chromosomes

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12
Q

when are chromosomes duplicated

A

before mitosis

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13
Q

what joins two sister chromatids

A

a centromere

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14
Q

how many STR loci do we look at in forensics

A

17

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15
Q

what are the 3 reasons individuals show genetic variation

A
  • genetic recombination
  • random assortment of chromosomes
  • random pairing of gametes
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16
Q

what is genetic recombination and when does it occur

Study These Flashcards
A

the exchange of genetic material between parental chromosomes that occurs during meiosis

17
Q

what is random assortment of chromosomes and when does it occur

Study These Flashcards
A

when chromosomes separate they all do it differently, resulting in four unique daughter gametes - occurs during meiosis 1

18
Q

what is random pairing of gametes

Study These Flashcards
A

mate choice in the physical act of fertilisation

19
Q

name the three reasons for genetic differentiation

Study These Flashcards
A
  1. Barriers to gene flow - migration
  2. Genetic drift - population size
  3. Natural selection - non-random mating
20
Q

describe a novel mutation

Study These Flashcards
A

the insertion or deletion of a base pair leading to changes in the triplet code for amino acids - frameshift

21
Q

what are point mutations

Study These Flashcards
A

transversion or transition

22
Q

what are the 3 processes involved in DNA extraction

Study These Flashcards
A
  1. Extraction - removal of DNA from cellular casing
  2. Purification - removal of inhibitors from DNA sample
  3. Isolation - capture of remaining DNA
23
Q

name 5 things needed for PCR

Study These Flashcards
A
  1. Thermal cycler
  2. Template DNA
  3. PCR primers
  4. DNA polymerase
  5. PCR buffer
24
Q

what are the three main steps of PCR

Study These Flashcards
A
  1. Denature
  2. Anneal
  3. Extend
25
describe the denaturing step in PCR
DNA melts because it is heated to 94 degrees or higher, causing the double stranded DNA to separate
26
describe the annealing step of PCR
the temperature is reduced to between 40-60 degrees, to allow primers to hybridise to complementary DNA
27
describe the extending step in PCR
the temperature is then increased to between 70-74 degrees (optimum temperature for DNA polymerase activity), so that DNA polymerase can make new DNA strands
28
how many primers are used to amplify a single DNA target region and what are they designed to do
2 - forward and reverse - designed to flank the target region for chopping
29
what does DNA analysis require
two samples - evidence and suspect sample
30
define DNA profile
a small set of DNA variations that is very likely to be different in all unrelated individuals
31
how long is an STR
2-6 bp
32
what makes STR's specific to individuals
the number of repeats at a specific loci
33
what do we use to analyse the length differences of STR's
capillary electrophoresis
34
what has to be looked at in order to prove that a DNA sample does or does not belong to someone
the probability that it would occur elsewhere in the population
35
how do we understand the probability that a DNA sample would occur elsewhere in a population
by looking at the frequency each allele exists at within and between populations - by measuring multiple genotypes within populations
36
how do we measure allele frequency
p + q = 1
37
why does forensic DNA profiling use more loci with higher polymorphism
as the probability of observing a matching profile is high when measuring he genotype frequency at a single locus with two alleles
38
why is accounting for population structure when calculating the probability of observing matching DNA important
as it prevents over and understating the evidence
39
name 4 ways matching DNA profiles can occur innocently
1. Mono-zygotic twins 2. Severely inbred populations (not human) 3. Instances of laboratory error 4. DNA transfer events - direct or indirect

forensic science (13 decks)

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