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#STR analysis

2 public questions tagged with this topic.

Molecular Marker

A STR on X chromosome shows unexpected allele. Likely cause:

X chromosome transmission shows characteristic patterns: sons receive X from mother, daughters receive X from both parents. STR allele unexplained by maternal or paternal haplotypes suggests new mutation altering repeat number rather than SNP interference or VNTR artifact. Microsatellite mutation rate is elevated due to replication slippage, generating novel alleles in germline. Maternal inheritance explains expected allele but not unexpected size variant. Therefore appearance of atypical X-linked STR allele most plausibly results from de novo mutation expanding or contracting repeat tract within X locus.

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 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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