Emerging Trends - Phenotyping

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  • Emerging Trends
    • DNA profiling developments
      • 1985 - Sir Alec Jeffreys published the first paper detailing DNA fingerprinting and how it could be used for identification purposes in biological samples
        • DNA is powerful identification tool than blood groupings and had a high discriminatory power
          • Initial method used by Jeffrey was difficult to perform in the lab and varying results were not obtained
            • Required a certain amount of DNA which meant it was not appropriate for many biological samples
              • Especially forensic samples which are often degraded
            • The sensitivity of the technique needed to be improved and by the end of the 1980s, DNA profiling had replaced DNA fingerprint, and the method of PCR had been developed.
              • Meaning that biological samples with smaller amounts of DNA could be analysed
                • Important for forensic science applications
      • Continued research into genetic mapping
        • Resulted in more polymorphisms being identified,, particular shorter repeat units of 2-6bp (STRs)
          • Several STRs could be combined into one analysis and fluorescent dyes allowed the fragments to be detected
      • Ability to store DNA profiles digitally
        • Allows easier comparison
      • Developments of Y-STRs and mtDNA profiling techniques
        • Familial, Paternity, missing persons and mass identification
      • Current techniques (DNA 17) are highly sensitive and discriminating
        • Can be used on degraded and difficult samples
    • Determining behavioural traits
      • Chromosome regions have been identified which might be linked to smoking, left handedness and stuttering
        • Not as easy to identify
    • Determining physical appearance
      • Phenotype
        • Coding regions of DNA
          • Insertion/deletions of bases or SNPs within a coding region can alter the proteins made and in some cases a phenotypic change can be observed
        • Phenotyping
          • Still in its infancy
            • Requires identification of SNPs within a gene or non-coding region that shows association with a particular trait
              • Lack of detailed understanding of the basis of natural human variation
                • Research funding tends to focus on disease-causing vairation
          • Complex traits
            • Determined by several genes, each with a small effect
              • Requires large genome-wide association studies to achieve statistical significance
          • Large environmental component
            • A lot of the variation cannot be captured in genetic tests and can make prediction less accurate
          • Ethical issues
            • High potential for mismatches
              • Stigmatisation
                • Privacy
            • One off observation (by the witness) vs. the storage of genetic information on a persons EVC for future use
              • Data becomes useable for different purposes
          • Charactersitics
            • Hair Colour
              • Melanin and melanosomes
                • HIrisPlex system for hair and eye colour - validation
                  • Only relevant in populations where there is variability in hair colouration
            • Eye Colour
              • Most accurately predicted EVC
                • Human traits with most variability in colour
                  • Defined by the amount of melanin and the number of melanosomes present
                    • Affects pigmentation
                      • Relies on finding an association between certain SNPs and particular eye colouration
            • Height and Age
              • Very low predictive value as almost 700 genes involved in determining height
                • Accumulation of mtDNA deletions and telomere shrinking
            • Skin
              • Most complex pigmentation phenotypes
                • Variability in skin colour is likely to have evolved as a response to UV intensities around the world
                  • Incomplete understanding of the genetics of skin pigmentation
      • Predicting externally visible characteristics can provide important information
      • Research began in 1990s
      • Investigative Value
        • At present, forensic DNA Phenotyping can only provide broad categorisations
          • cannot be used for identification purposes
            • value in generating investigative leads
              • Limited however due to possibility of traits being altered

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