#DNA profiling

Molecular Marker

Which STR property makes it ideal for forensic testing?

Forensic identification demands markers with many alleles, high heterozygosity, small amplicon size suitable for degraded DNA, and uniform genomic distribution. Short Tandem Repeats fulfill these criteria because replication slippage generates extensive polymorphism, with heterozygosity often exceeding 70 percent. Multiple unrelated individuals rarely share complete STR profiles, giving high power of discrimination and low random match probability. Low mutation rate or stability would reduce informativeness, while low assay cost is beneficial but not primary. High polymorphism ensures uniqueness of profiles, essential for criminal casework and parentage testing.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

STRs are primarily used in:

Short Tandem Repeats exhibit 1-6 bp repeat units with high mutation rates due to strand slippage, creating many alleles per locus and high heterozygosity. This hypervariability, combined with codominant inheritance, low DNA requirement, and amenability to multiplex PCR, makes them exceptionally discriminating for individual identification. Forensic genetics, paternity testing and kinship analysis rely on standardized STR panels such as CODIS loci. STRs are not primary tools for DNA synthesis, sequencing chemistry or protein expression; their power lies in resolving identity and relatedness through polymorphic length variation.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which molecular marker is used in forensics for individual identification?

Short tandem repeats are hypervariable loci composed of two to six base pair repeats with numerous alleles in populations, high heterozygosity and low mutation stability suitable for human identification. Their small amplicon size allows analysis from degraded DNA samples, multiplex PCR enables simultaneous typing of fifteen to twenty loci, generating a unique genetic profile with extreme discriminatory power. RFLP requires large DNA amounts, SNP panels are biallelic and less discriminatory per locus, while ISSR lacks standardized forensic databases and reproducibility.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

In STRs, what varies among individuals?

Short tandem repeats comprise tandem arrays of two to six base pair motifs where individual variation derives from different copy numbers of the repeat unit at a given locus. DNA polymerase slippage during replication expands or contracts repeat tracts, creating alleles differing in length but not in base composition or methylation pattern. Enzyme activity is unrelated to structural polymorphism. Consequently, genotyping relies on measuring fragment length variation through capillary electrophoresis, reflecting inherited differences in repeat number critical for forensics and paternity testing.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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