Crime Scene And Trace Evidence Flashcards
What is DNA profiling ?
process of extracting DNA to determine an individuals DNA characteristics
Which cell stores the full genetic program of a person ?
Red blood cells
How else, apart from identifying a suspect can DNA be used ?
To exonerate a suspect
Where is DNA contained ?
In the nucleus
What does DNA contain ?
Genetic instructions for development and functioning
What is the structure of DNA ?
-double helix
-2 anti parallel strands wound around each other
-sugar phosphate backbone connected via hydrogen bonds
-complementary based pairs (A-T, G-C)
Who pieced together all the information on DNA in 1952 ?
Watson and crick
What are the four different bases of DNA ?
Adenine, Thymine, Guanine and Cytosine
What are the components of a nucleotide ?
Sugar (deoxyribose), phosphate group and nitrogenous base
What are histones ?
Proteins found in the nuclei which package and help order the DNA in nucelosomes
What is chromatin ?
Complex of DNA and proteins that make up chromosomes ( the form in which the DNA is packaged within the nucleus)
How is DNA as a euchromatin ?
Less condensed and more accessible
How is DNA as a heterchromatin ?
More condensed and less accessible
What is a chromosome ?
Thread like structure that consists of a long strand of DNA, carrying hundreds or thousands of genes, completely wound around and packaged with proteins
What is a Karyotype ?
Total set of chromosomes
What did Sir Alec Jeffreys discover ?
Mini satellites
What is a mini satellite ?
Segments that vary in size and composition from individual to individual and had no apparent function
What are variable number tandem repeats (VNTR) ?
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
What are the two types of VNTR ?
Mini- satellites: 10-200 base pairs
Micro-satellites: 2-9 base pairs
What is restriction fragment length polymorphism (RFLP ) ?
- 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
What is used instead of RFLP ?
Short tandems repeats (STRs) as they’re more practical
What is polymerase chain reaction (PCR) ?
-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
How many cycles in PCR ?
25-30 depending on sample type and kit used
Who invented PCR ?
invented in 1984 by Kary Mullins
What is SNP ?
When errors occur in replication and are not corrected
What is NGS ?
Full genome mapping which uses different methods of sequencing and can analyse multiple combinations of markers in tandem
What are short tandem repeats (STR) ?
STRs are highly polymorphic and are inherited from each parent
What does presumptive testing involve ?
-identifies substance
-often colorimetric
-sensitive, less specific
-fast, cheap, easy to
What does confirmatory testing involve ?
-identifies exact substance
-analytical method, highly specific
-time-consuming, expensive
-complex, requires specific setup
-stringent quality checks
What are the order of events for DNA profiling ?
-sample receipt
-extraction
-quantification
-amplification
-electrophoresis
-analysis
-interpretation
-reporting
-court
What are the key steps for the extraction and purification of DNA ?
-burst cell membrane to release DNA
-separate DNA from proteins and other cellular compounds
-cleaning the DNA
What are the most common methods for purification of DNA ?
-organic based
-silica based
-paramagnetic beads
What are the common methods for quantification of DNA ?
-UV spectrophometry
-fluorescence spectrophotometry
-hybridization
-real time PCR
What is quantification of DNA ?
Measurement of concentration of DNA
What PCR kit is used in the UK ?
DNA17
What are the different types of electrophoresis ?
Gel and capillary
How does gel electrophoresis work ?
Uses agarose or polyacrylamide gel
-DNA fragments separated by size
-Slower but can handle larger samples
-Visualized using UV light and dyes
How does capillary electrophoresis work ?
Uses thin glass capillaries filled with polymer
-Faster and more sensitive than gel
-Automated process
-Laser detection of fluorescently labelled DNA
What are the differences between gel and capillary electrophoresis ?
-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
What happens when an individual is arrested by the police ?
A DNA sample is taken and sent to an accredited lab who amplify and catalogue the sample
What samples does the national DNA database contain ?
-reference samples
-crime scene samples
-missing persons
-contamination elimination Db
-separate- staff elimination Db
What are the different types of DNA matches ?
-full
-partial
-familial
What are limitations of DNA evidence ?
-potential for contamination
-interpretation challenges with partial profile/ mixed samples
-importance of context in DNA evidence
-degradation of DNA
-transfer and persistence issues
What are ethical considerations in DNA profiling ?
-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
What is IoT ?
Internet of things- any device that has the ability to connect to the internet
What is the fundamental problem of cyber security ?
Not understanding the problem
What is binary ?
Computers store data in 0 and 1s
What are the two types of encryption ?
Symmetric and asymmetric
What are the common uses of symmetric encryption ?
-Secure messaging apps
-file encryption software
-bitlocker
What are the common uses of asymmetric encryption ?
-secure email protocol
-digital signatures for documents authenticity and integrity
-secure key exchange and establishment of SSL/TLS protocol for secure websites
What are the three factors of authentication ?
- something you know (pin)
-something you have (device)
-something that proves who you are (fingerprint)
What is the role of police in a criminal enquiry ?
Police and Criminal Evidence Code of Practice paragraph 3.5, 1984
-The investigator should pursue all reasonable lines of inquiry, whether these point towards or away from the suspect.
What software is used to extract data from electronic devices ?
-belkasoft
-cellebrite
-grayshift
What are the ethical issues surrounding data access ?
-collecting data that is irrelevant
-retention of data
What is forensic entomology ?
The study of insects and other arthropods in legal context
What are the three main areas of entomology ?
-urban
-stored products
-medico-legal
What are the applications of medico-legal entomology ?
-fraud
-blackmail
-contamination of food stuff
-illegal importation
-delusory parasitosis
-criminal activity
When was entomology first used in the UK ?
1935- case of Dr Buck Ruxton
-killed his wife and her maid
-chopped up their bodies and wrapped them up in newspaper before disposing of them in Scotland
-larvae established when the bodies were deposited
What are necrophagous species ?
Feed on decaying flesh
What bug is the first to colonise the body ?
Blowflies
What feeds on the dry remains of the body ?
ham beetles
What are considered the secondary colonisers of the body ?
Rove beetles
What are omnivorous species ?
Feed on the body such as wasps and ants
What are adventive species ?
Use the body as a habitat
Why is blowfly larvae important ?*
-most common on cadaver
-most rapid colonisers
What is the life cycle of a blowfly ?
-eggs
-1st instar larvae
-2nd instar larvae
-3rd instar larvae
-poparia containing puparia
-adult fly emerging from puparia
-adult blowfly
What is oviporous
Eggs laid which hatch into larvae
What is ovoviviporous ?
Eggs laid containing developed larvae
What is larviporous ?
Larvae laid (live)
What does measuring larval mass temp do ?
Help know which development stage larvae is in.
What is used to measure larval mass temp ?
Infrared data logger
How can you tell if 3rd instar larvae is feeding or post feeding ?
-if the food is still in the crop (stomach)
-if it was collected from the body or the surrounding area
What is maggot therapy ?
Using specific maggots in a bag to feed on dead skin to clean wounds
What is ADH ?
Accumulated degree hours
How is ADH calculated ?
Time x temperature
What can be used instead of ADH ?
ADD (accumulated degree days)
