Biological Evidence Flashcards
What are mitochondria ?
Cellular organelles responsible for energy production through oxidative phosphorylation
Where are mitochondria located ?
Cytoplasm
How many genes do mitochondria have ?
37
what is the inheritance pattern of mitochondrial DNA ?
MtDNA is inherited exclusively from the mother. All maternal relatives share the same mtDNA sequence
When was mtDNA fully sequenced ?
1981
What are the advantages of using mitochondrial DNA ?
-high copy number: each cell contains hundreds of thousands of mitochondria
-maternal linage tracing: allows for identification of maternal relatives across generations
-databases can be created
What are the limitations of using mitochondrial DNA ?
-lack of individuality: mtDNA is shared among all maternal relatives across
-Heteroplasmy: the presence of multiple mtDNA types within an individual, which can complicate interpretation
Where is the most mitochondria most likely to be found ?
The more energy the tissue requires the more mitochondria
What are mitochondria critical for ?
Cellular metabolism and function
What is Sanger sequencing ?
-uses single-stranded DNA template, primer, DNA polymerase, ddNTPs and fluorescent labels
-ddNTPs terminate DNA extension and emit specific wavelengths of light
-sequence determined by electrophoretic separation
What is the Y chromosome ?
One of the two sex chromosomes in males
What is the Y chromosome characterised by ?
- approximately 60 million base pairs
-contains 200 genes
-passes exclusively from father to son
-highly stable
What is the inheritance pattern of the Y chromosome ?
Inherited only through male lineage, sons receive Y-chromosome from their fathers
What are the advantages of using Y chromosomes ?
-tracing paternal lineages
-male-specific, allowing for isolation of male DNA in mixed samples
What are the limitations of using Y chromosomes ?
-lack of individuality: shared among male relatives
-limited genetic diversity compared to autosomal markers
What is the difference in lineage markers ?
Autosomal- passed on in part from all ancestors
Y-chromosome- passed on complete but only by sons
Mitochondrial- passed on complete but only by daughters
What is LMD (laser micro-dissection)
-isolates sperm cells from microscope slides
-allowing re-analysis
-effectively separates sperm from mixed cell types without loss of male material
What is LCN an extension of ?
SGM plus (10 autosomal loci + sex marker)
What are the different techniques used in LCN ?
-increased PCR cycles
-enhanced detection methods
What are the PCR cycles increased to in LCN ?
From 28-30 to 34-35
What are limitations of LCN ?
-require careful handling to avoid contamination
-increased risk of contamination can lead to false positives
-incorrect or misleading results can complicate interpretation
What are common biological fluids in forensics ?
-blood
-saliva
-semen
-vaginal secretions
-urine
What are the identification methods for biological fluids ?
-immunological tests/ chemical tests
-molecular methods
-RNA-Based methods
What are spectroscopic techniques of bodily fluid analysis ?
-Raman Spectroscopy: Analyses light scattering to create complex spectra for fluid identification; variability observed with aging bloodstains.
-Fourier Transform Infrared (FT-IR) Spectroscopy: Evaluates biological fluids while accounting for environmental contamination.
What are emerging technologies of bodily fluid analysis ?
-DNA Methylation Patterns: Examines methylation at specific genomic sites to identify tissue origin and estimate age.
-Microbiome Analysis: Studies microbial communities to provide additional context in forensic investigations.
What are the principles of DNA phenotyping ?
Involves analysing genetic information to predict physical traits and ancestry from biological samples, such as hair, saliva or blood
What does the process of DNA phenotyping use ?
Specific genetic markers associated with traits like eye colour, hair colour and skin pigmentation
What are the limitations of genetic phenotyping ?
-DNA phenotyping cannot provide definitive identification; it narrows down possibilities rather than pinpointing a specific individual.
-Environmental factors and gene interactions can influence physical traits, leading to uncertainty in predictions.
What are the ethical considerations of DNA phenotyping ?
-Potential misuse of genetic information for profiling individuals based on appearance.
-Concerns about privacy and consent when using genetic data for non-medical purposes.
-Regulatory frameworks vary by country; some nations have strict guidelines on the use of DNA phenotyping in forensic investigations.
What is the current application of DNA phenotyping ?
Used in criminal investigations to generate leads when traditional DNA profiling does not yield results and assists law enforcement in narrowing down suspect list
What is the future potential for DNA phenotyping ?
-Advances in genomic research may improve accuracy and expand the range of predictable traits.
-Integration with other forensic techniques could enhance investigative capabilities.
What is a cold case ?
A criminal investigation that remains unsolved after an extended period of time- usually years or decades after the original crime occurred
What types of crimes are cold cases usually?
- murders
-sexual assaults
-missing persons
What are cold cases due to ?
-lack of leads/ suspects
-lack of evidence
-technological limitations
Where can you find information about cold cases in the UK ?
On each police forces website
Where can you find information about cold cases in the UK ?
On each police forces website
What was the most popular method of killing for unsolved homicides in London ?
Sharp instrument
What skills are needed for an officer working cold cases ?
-tenacity
-patience
-attention to detail
-communication
-impartiality
What approach is taken for cold cases investigations ?
A systematic approach where case information and material is reviewed and emulation of historic methods
What material must be reviewed ?
All available information which is usually done by multiple experts, detectives and other key staff
What exhibits to the police retain ?
-photographs
-paperwork- witness statements and interview transcripts
-medical reports
-PM reports
What considerations should the police have when retaining information for cold cases ?
-the retention time
-type of crime
-returned to force or not
What material is contained within the forensic archives for cold cases ?
-sub-exhibits- microscope slides, tapings, debris, cuts of fabrics, etc
-swabs from samples or from medical examinations
-extracts prepared during examinations
DNA extracts
How are historic methods evaluated ?
-understand the context of the original investigation focusing on the technology at that time
-review the methods - limitations etc
- identify potential for re-examination with modern techniques
What is the forensic review process for sexual offences ?
- tend to be DNA focused
-tend to utilise FSS paperwork and historic retained materials
-suited to large-scale review projects
-well-established process
What is the forensic review process for homicides ?
-rarely straightforward
-often numerous materials and documents to consider
-multiple evidence types
-reinterpretation/reexamination
-staged strategy
What are the challenges of cold cases ?
-deceased victims
-no paperwork
-availability of exhibits depends of age of crime
- understanding of initial handing of evidence for court
-scientists in labs didn’t always use disposable lab coats, wear gloves or have masks or hair nets
-who has handles the evidence
How is re-examination if semen done ?
Using improved spermatozoa recovery techniques
How is examination of blood done ?
-luminol
-low power microscopy
How is DNA analysis carried out ?
-Now 16 or 23 areas of DNA (plus sex marker) – thus more discriminating
-Automated
-Better ‘chemistries’ + different ‘kits’
-Increased sensitivity
-Replaces current test including low template
-Fully compatible with NDNAD
-Quantification
What are the challenges with extraction ?
Bone/Teeth
Formaldehyde treated tissues
Paraffin embedded tissue/Wax histology block
Slides – preferential lysis or not
What do familial searches require ?
An almost complete DNA profile
What does a familial searches generate ?
2 lists-
- parent/ child
-siblings
How does next generation sequencing work ?
- DNA polymerase allows for the incorporation of fluorescently labelled dNTPs into a DNA template strand during sequential cycles
-the nucleotides are identified by fluorophore excitation
What are the 4 types of NGS ?
-sequencing by synthesis
-pyrosequencing
-sequencing by ligation
-ion semiconductor sequencing
What type of NGS does forensic analysis use ?
Sequencing by synthesis
How does NGS work ?
-library preparation
-cluster generation
-sequencing
-data analysis
What is the difference between NGS applications and forensic genomic applications ?
Forensic genomic applications use a targeted sequencing approach
What are the steps of library preparation for NGS ?
-The input DNA is fragmented using ultrasonication or enzyme digestion
-The end of the fragment strands are then end repaired with either the addition of complimentary nucleotides or removal of excess nucleotides
-These fragments are the bimolecularly prepared to be attached to the sequencing material
What is cluster generation ?
-During cluster generation, the library is injected into a flow cell where fragments are captured on a lawn of surface-bound oligos complementary to the library adapters.
-Each fragment is then amplified into distinct, clonal clusters through bridge amplification.
-With cluster generation complete, the templates are ready for sequencing.
How is DNA sequenced in NGS ?
-This method works by attaching a singular complimentary base (dNTP) to the target fragment per cycle
-Once attached a florescent emission occurs and detected
-After each cycle of base attachment, the remaining excess are washed away
-This then repeats with as a new base is attached
How is data analysed for NGS ?
-the sequence reads are aligned to a reference genome in the library
-Following alignment, different types of analysis are possible such as single nucleotide polymorphism (SNP), STR typing, mtDNA analysis, phylogenetic or metagenomic analysis, and more.
What is the information generated from NGS known as ?
Reads
What is the application of NGS in forensics ?
-It includes over 200 genetic markers that can be assessed at once, removing the need for different multiplexes currently used
-It allows for both STR and SNP analysis at the same time
-Provides phenotypic-informative SNPs giving estimates of eye colour and hair colour, as well as biogeographical ancestry-informative SNPs.
-Forensic Investigations dealing with profiles of unknown individuals therefore all extra information is valuable
What is rapid DNA analysis ?
Rapid DNA is a fully automated process of developing a DNA profile from a mouth swab. This happens in 1-2 hours—without the need for a DNA laboratory or any human intervention and review.
What does rapid DNA system consist of ?
-swab
-a cartridge
-instrument
-analysis software
What instruments are used in rapid DNA system?
RapidHIT DNA
ANDE 6C
How does RapidHIT ID work ?
-one sample
-one minute hand on time
-generates data compatible with DNA databases around the world
-designed for low conc samples
How does ANDE 6C work ?
- A chips can process 5 high conc samples
- I chips can process 4 low conc samples
-generates data compatible with DNA databases around the world
-used in US
What are the pros of rapid DNA ?
-In custody processing for NDNAD loads
-fast and simple evidence processing
-missing persons investigations- fats processing of human remains
- border force- dna profiles from detainees for comparisons to indices for prior border crosses
What are the cons of rapid DNA ?
-not capable of adjustments and optimizations
-cannot rework samples
-re-sampling might be needed and might not always be possible
What is latent fingerprinting ?
-synthesised from jellyfish
-green fluorescent protein chromophore from amino acids bind selectively to negative molecules in fingerprints thus emitting a fluorescent glow
What are the pros of latent fingerprinting ?
-water soluble
-low cytotoxicity
-no effect on DNA
-portable system with wide range
