Interpretation of DNA Profile Match by Mix STR Tool in Crime Scene Investigation

Author Name: *Amaani Tasneem
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DNA evidence is being increasingly used in court cases. The first DNA typing methodology used forensically required comparatively large amounts of starting material. Now, with the use of the polymerase chain reaction (PCR) to amplify Short Tandem Repeat (STR) segments of DNA, laboratories are able to analyze DNA from samples as small as a single cell. The high levels of variability that exist at STR loci make them well-suited for use in human identification. There is a great deal that a defense lawyer can and must do in order to effectively represent a client who is incriminated by DNA evidence. Interpretation of multiple DNA profile matches was performed by mix STR tool where in the samples was collected from a homicide crime occurred at the construction site. Alleles of 15 different locus approved under CODIS namely FGA, TPOX, D8S1179, vWA , D2S1338, D19S433, D18S51, D21S11, THO1, D3S1358, AMEL, CSF1P0, D16S539, D7S820, were retrieved for each of the Victim, Suspect, and the Evidence involved in the crime. These samples with their known alleles were analyzed thoroughly by MIX STR TOOL with which we can trace out the culprits and mislabeling during sample collection involved in the crime by getting accurate information on the percentage of match by determining the presence or absence of alleles in the given data.


Forensic science is any science used for the purposes of the law, and therefore provides impartial scientific evidence for use in the courts of law, and in a criminal investigation and trial. Bioinformatics and forensic DNA are inherently interdisciplinary and draw their techniques from statistics and computer science bringing them to bear on problems in biology and law. Personal identification and relatedness to other individuals are the two major subjects of forensic DNA analysis. One of the most contentious issues in forensic use of DNA evidence is how to estimate the probability that two DNA profiles match by chance. In order to determine the probability that a particular genotype might occur at random in a population, extensive population data must be gathered to make an estimate of the frequency of each possible allele and genotype. A sample size much larger than 100 samples is needed to make reliable projections about a genotype’s frequency in a large population. Given allele frequencies, DNA profiles are screened automatically for matches between profiles of person to person(s), person to scene(s) and scene to scene(s). Although the most used set of STR loci are spread on all the chromosomes, they have different mutation rate. The adage “every contact leaves a trace” indicates the importance of a technique able to type trace amounts of genetic material left during the commission of a crime. This genetic information can then be used to include or exclude suspects as being the source of the genetic material. Forensic analysis involves the testing of regions of an individual’s DNA.Databases have been compiled which list the abundance of a particular fragment of DNA in the population. From this information, an estimate of the abundance of combinations of DNA at several regions can be made and compared to the DNA of victims or suspects.


The given samples were analyzed and suspect number 10 whose sample was run on Lane 11 and Suspect number 18 whose sample was run on Lane 19 were found to be the prime culprits involved in the murder of the civil engineer at the construction site. The following interpretations were helpful in investigation and conclusion:
1. As per Rep EE Evidence no.E1, E2, E5,E6,E10,E18 are matching with one another and hence belong to one person, evidence no E3,E7,E9,E14,E16,E19 are matching with one another and not with any other evidence, hence they belong to any other person while evidence no E4,E8,E12,E20 are matching with one another and not with any other evidence, hence they belong to any third person. 2. As per Rep SE victim’s sample was matching with evidence E1,E2,E5,E6,E10,E18 Suspect 10 with evidence E3,E7,E9,E14,E16,E19 and suspect18 with evidence E4,E8,E12,E20. 3. When evidence by evidence analysis was done it was observed that there were four evidences E11, E13, E15, E17 that did not match with any of the Standard sample, hence belong to any Third culprit whose profile was absent from the suspects.

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