how is DNA analysis in criminal investigations performed?

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how is DNA analysis in criminal investigations performed?

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they search for biological evidences like hair , nail , skin etc. That evidence contains unique DNA strand of perp . Then they take the sample from suspect of the hair , skin , and they try to match the sample dna with the dna they found at crimescene. If it matches , then you have your perpetrator

Our DNA is made of many many genes interrupted by intronic or non coding sequences (within and between them). There are, however, small differences between people, due to mostly lineage, and sometimes mutations. A big example are single nucleotide polymorphisms. These are differences in one nucleotide (e.g. Instead of sequence AG**A**GCTA you could have AG**G**GCTA). If this change does not alter the gene product at all or at least not functionally, then it becomes a common site for a population to have variability in: due to codon degeneracy, we have many codons for a given amino acid, so in my example acruslly both AGA and AGG code for arginine (an amino acid), so such a change still produces the same amino acid and therefore the exact same resulting protein. Other times, the amino acid property is all that matters for function, so if you change it to another similar one (e.g. both water loving or hydrophilic and both can be phosphorylated like serine and threonine), then the function is unaffected even though the amino acid changed. We know a lot of these loci (places on the genome) that vary from person to person. When they do genetic analysis to see if it’s the same person as a known suspect, they don’t actually sequence the whole genome, that’s too expensive, complicated and takes a bit of time and expertise, they actually do quick analysis at many such spots (for paternity tests for example, around 12 or so, but I don’t know how many loci for forensics). If they find the suspect and the sample share all the SNPs, then the chances they’re different people is like one in several hundred million, so they consider them the same person. The more loci they look at, the higher the confidence in the result that they’re the same person.