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Introduction To Forensic Science > Crime Scene And Trace Evidence > Flashcards

Crime Scene And Trace Evidence Flashcards

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1
Q

What is DNA profiling ?

A

process of extracting DNA to determine an individuals DNA characteristics

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2
Q

Which cell stores the full genetic program of a person ?

A

Red blood cells

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3
Q

How else, apart from identifying a suspect can DNA be used ?

A

To exonerate a suspect

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4
Q

Where is DNA contained ?

A

In the nucleus

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5
Q

What does DNA contain ?

A

Genetic instructions for development and functioning

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6
Q

What is the structure of DNA ?

A

-double helix
-2 anti parallel strands wound around each other
-sugar phosphate backbone connected via hydrogen bonds
-complementary based pairs (A-T, G-C)

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7
Q

Who pieced together all the information on DNA in 1952 ?

A

Watson and crick

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8
Q

What are the four different bases of DNA ?

A

Adenine, Thymine, Guanine and Cytosine

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9
Q

What are the components of a nucleotide ?

A

Sugar (deoxyribose), phosphate group and nitrogenous base

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10
Q

What are histones ?

A

Proteins found in the nuclei which package and help order the DNA in nucelosomes

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11
Q

What is chromatin ?

A

Complex of DNA and proteins that make up chromosomes ( the form in which the DNA is packaged within the nucleus)

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12
Q

How is DNA as a euchromatin ?

A

Less condensed and more accessible

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13
Q

How is DNA as a heterchromatin ?

A

More condensed and less accessible

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14
Q

What is a chromosome ?

A

Thread like structure that consists of a long strand of DNA, carrying hundreds or thousands of genes, completely wound around and packaged with proteins

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15
Q

What is a Karyotype ?

A

Total set of chromosomes

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16
Q

What did Sir Alec Jeffreys discover ?

A

Mini satellites

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17
Q

What is a mini satellite ?

A

Segments that vary in size and composition from individual to individual and had no apparent function

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18
Q

What are variable number tandem repeats (VNTR) ?

A

Parts of the genome is made of short sequences of DNA which repeat in tandem
- the number of repeats for each unrelated individual is highly variable

19
Q

What are the two types of VNTR ?

A

Mini- satellites: 10-200 base pairs
Micro-satellites: 2-9 base pairs

20
Q

What is restriction fragment length polymorphism (RFLP ) ?

A
  • genomic DNA is treated with restriction enzymes which cut DNA at a certain specific sequence of bases
    -each restriction enzyme cuts in a unique restriction site
    -results in several fragments of DNA in varying lengths
    -placed on gel and an electric current is applied
    -results in a pattern of bands
21
Q

What is used instead of RFLP ?

A

Short tandems repeats (STRs) as they’re more practical

22
Q

What is polymerase chain reaction (PCR) ?

A

-has 3 distinct stages: denaturation, annealing and extension
-denaturation: 96 degrees for 5-15s
-Annealing: 60 degrees for 35-60s
-Extension: 75 degrees for 5-60s

23
Q

How many cycles in PCR ?

A

25-30 depending on sample type and kit used

24
Q

Who invented PCR ?

A

invented in 1984 by Kary Mullins

25
Q

What is SNP ?

A

When errors occur in replication and are not corrected

26
Q

What is NGS ?

A

Full genome mapping which uses different methods of sequencing and can analyse multiple combinations of markers in tandem

27
Q

What are short tandem repeats (STR) ?

A

STRs are highly polymorphic and are inherited from each parent

28
Q

What does presumptive testing involve ?

A

-identifies substance
-often colorimetric
-sensitive, less specific
-fast, cheap, easy to

29
Q

What does confirmatory testing involve ?

A

-identifies exact substance
-analytical method, highly specific
-time-consuming, expensive
-complex, requires specific setup
-stringent quality checks

30
Q

What are the order of events for DNA profiling ?

A

-sample receipt
-extraction
-quantification
-amplification
-electrophoresis
-analysis
-interpretation
-reporting
-court

31
Q

What are the key steps for the extraction and purification of DNA ?

A

-burst cell membrane to release DNA
-separate DNA from proteins and other cellular compounds
-cleaning the DNA

32
Q

What are the most common methods for purification of DNA ?

A

-organic based
-silica based
-paramagnetic beads

33
Q

What are the common methods for quantification of DNA ?

A

-UV spectrophometry
-fluorescence spectrophotometry
-hybridization
-real time PCR

34
Q

What is quantification of DNA ?

A

Measurement of concentration of DNA

35
Q

What PCR kit is used in the UK ?

A

DNA17

36
Q

What are the different types of electrophoresis ?

A

Gel and capillary

37
Q

How does gel electrophoresis work ?

A

Uses agarose or polyacrylamide gel
-DNA fragments separated by size
-Slower but can handle larger samples
-Visualized using UV light and dyes

38
Q

How does capillary electrophoresis work ?

A

Uses thin glass capillaries filled with polymer
-Faster and more sensitive than gel
-Automated process
-Laser detection of fluorescently labelled DNA

39
Q

What are the differences between gel and capillary electrophoresis ?

A

-Resolution: Capillary offers higher resolution
-Speed: Capillary is faster (30-60 minutes vs. hours)
-Sample size: Gel can handle larger samples
-Automation: Capillary is fully automated

40
Q

What happens when an individual is arrested by the police ?

A

A DNA sample is taken and sent to an accredited lab who amplify and catalogue the sample

41
Q

What samples does the national DNA database contain ?

A

-reference samples
-crime scene samples
-missing persons
-contamination elimination Db
-separate- staff elimination Db

42
Q

What are the different types of DNA matches ?

A

-full
-partial
-familial

43
Q

What are limitations of DNA evidence ?

A

-potential for contamination
-interpretation challenges with partial profile/ mixed samples
-importance of context in DNA evidence
-degradation of DNA
-transfer and persistence issues

44
Q

What are ethical considerations in DNA profiling ?

A

-privacy concerns with databases
-familial searches and implications
-consent issues in mass screening
-potential for genetic discrimination
-ownership and storage of genetic information
-use of DNA for purposes beyond criminal investigation

Introduction To Forensic Science (5 decks)

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