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#SNPs

3 public questions tagged with this topic.

Molecular Marker

SNPs are typically:

Single Nucleotide Polymorphisms arise from single base substitution, insertion or deletion at a defined genomic coordinate. Each SNP represents one locus with typically two alleles, following Mendelian segregation, and heterozygotes display both alleles simultaneously, defining codominance. SNPs are not multilocus like RAPD or AFLP where many loci amplify together, nor dominant where heterozygote cannot be distinguished. They are not repetitive DNA and are usually bi-allelic rather than multiallelic. Their abundance, stability and codominant single-locus nature makes them ideal for association mapping and high-density genotyping.

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

SNPs are:

Single nucleotide polymorphisms represent the most abundant class of genomic variation, occurring every few hundred base pairs across genomes, numbering millions in humans and economically important plants. They are codominant in nature, discriminating homozygous and heterozygous states through allele-specific assays, sequencing or array hybridization platforms. Though individually less polymorphic than multiallelic SSR, their high density, amenability to automation and high-throughput genotyping makes them exceptionally powerful. Their use extends far beyond forensics, encompassing association mapping, genomic selection, evolutionary genetics and marker-assisted breeding programs worldwide.

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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Restriction Digestion & Mapping

SNPs affect restriction sites by:

Restriction enzymes recognize specific palindromic sequences of four to eight nucleotides with high precision. A single nucleotide polymorphism altering even one base within this motif abolishes hydrogen bonding complementarity needed for enzyme binding and catalysis, preventing phosphodiester hydrolysis. The enzyme no longer recognizes mutant site, so digestion pattern changes, forming basis for restriction fragment length polymorphism analysis. The site does not become shorter or more cleavable, nor does polymorphism inherently add labels. Loss of cleavage explains RFLP markers linked to disease mutations.

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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