#microsatellites

Molecular Marker

Microsatellites are also known as:

Microsatellites consist of 1-6 base pair motifs tandemly repeated 5-50 times, dispersed throughout eukaryotic genomes. DNA polymerase slippage during replication creates extensive length polymorphism, making them multiallelic and highly informative. In molecular marker terminology, this class is designated as Simple Sequence Repeats (SSR) and Short Tandem Repeats (STR), whereas VNTR refers to minisatellites of 10-100 bp. SNPs involve single-base substitutions and ESTs are partial cDNA sequences. Thus microsatellite nomenclature aligns with STR, widely applied in forensic profiling and genetic mapping.

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

Microsatellites vary in:

Microsatellites consist of tandemly repeated units of one to six base pairs dispersed throughout genomes. Variation among individuals originates from difference in copy number of repeat motifs at orthologous loci, caused by replication slippage leading to expansion or contraction of repeats. Base composition of repeat motif remains constant, for example CA dinucleotide, and genomic location is conserved. Length variation is secondary consequence of repeat number change. Therefore, allelic diversity at microsatellite loci directly reflects hypervariability in number of repeat iterations.

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 type of repeat unit is

Satellite DNA is classified by repeat unit size and total array length. Microsatellites, also called simple sequence repeats, contain repeat motifs of one to nine base pairs, typically one to six, arranged in tandem arrays of less than one hundred base pairs total length. Their small unit size distinguishes them from minisatellites where repeat units span ten to sixty base pairs and macrosatellites with hundreds of base pairs. Indels are not tandem repeats but insertions or deletions, differing fundamentally in origin and structural organization.

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 region in a microsatellite is non-coding and less conserved?

Expressed sequence tags derived from cDNA include both 5 prime and 3 prime regions. The 5 prime EST corresponds to coding sequence and highly conserved domains under strong purifying selection, showing lower polymorphism and sequence conservation across species. The 3 prime EST encompasses 3 prime untranslated region, often non-coding, less constrained evolutionarily, accumulating more variations including microsatellite repeats. Therefore, SSR mining in 3 prime EST yields greater polymorphism for marker development. Promoter regions regulate transcription and introns are spliced non-coding sequences outside EST terminology.

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

The most polymorphic marker system is:

Simple sequence repeats exhibit exceptional polymorphism due to high mutation rates caused by slipped-strand mispairing during DNA replication. Variable repeat numbers generate many alleles per locus, often exceeding ten in diverse germplasm, providing high polymorphic information content and heterozygosity values. Their codominant, multiallelic nature surpasses biallelic SNPs, low polymorphism RFLPs and dominant RAPD markers that detect fewer loci. Widespread genomic distribution, excellent reproducibility and ease of PCR detection further enhance utility for linkage mapping, population structure and fingerprinting studies in crop plants.

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

Microsatellites are also called:

Microsatellites consist of short tandemly repeated DNA motifs of one to six base pairs, such as dinucleotide CA repeats, repeated five to fifty times. They are also termed simple sequence repeats because of this simple, repetitive organization. Their high mutation rate through DNA polymerase slippage during replication creates extensive length polymorphism. VNTR includes minisatellites with longer repeat units of ten to sixty base pairs, SNP denotes single base changes, and indels represent insertion-deletion polymorphisms, all structurally different from microsatellite architecture.

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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