Lineage Markers

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  • Lineage Markers
    • Y- Chromosomes
      • Passed from father to son
        • Is only found in males
          • Helpful in crimes that involve males
        • Sex Chromosome
          • Non-recombining
      • The second smallest chromosome with a length of approximately 60 millions nucleotides.
        • Y chromosome testing is important
          • Forensic evidence examination
          • Paternity tests
          • Migration patterns
          • Y-STRs are found on the Y-Chromosome
            • When a profile is found to match, the significance needs to be assessed.
              • Done through the frequencies of Y-STR haploid types in the population
                • Counting method - use of databases
            • 400 Y-STR loci have been mapped along the chromosome, but only a small set of core loci have been analysed.
      • Random mutations are the only mechanisms for variations
        • Need to be considered to prevent false exclusions
    • mtDNA
      • Passed from mother to child
        • An organelle in the cytoplasm of eukaryotic cell.
          • Contains its own genome from the mum
            • Circular
            • Smaller than a nuclear genome
            • During conception, only the sperms nucleus enters the egg and joins directly with the eggs nucleus
              • The sperm does not contribute other celluar components
        • High copy number
          • Mitochondria has loads of copies of DNA of the mitochondrial genome
            • Nuclear DNA only has 2 copies of DNA
            • High probability of obtaining a DNA typing result from mtDNA
      • Hyper Variable Regions
        • 2 main regions that are focused on in forensics
          • HV2
      • Use of mtDNA
        • maternal inheritance is not unique to the individual and therefore when there are no direct relatives for a reference sample other relatives can  be used
          • Historical cases
        • If there is more than one difference in samples, then this is inconclusive.
          • This is because there is only on mutation in bases,
            • Little discrimination between the mtDNA sequences of the same maternal lineage
      • Methods of analysis
        • Determination of haplotype frequency
        • Comparison with a reference sample
        • Sanger sequence
    • Transferred directly from generation to generation without changing.
      • Exceptions with mutation
      • Do not follow menedlian inheritance
      • Do not recombine
    • Genetic information is referred to as a haplotype rather than a genotype because there is only a single allele per individual.


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