In-depth Notes on SNP Genotyping Technologies

Importance of SNP

SNP, or single nucleotide polymorphism, is a variation at a specific nucleotide position in the genome. It accounts for DNA variations among individuals, with a frequency of approximately one in every 1,000 base pairs (BP). SNPs play a crucial role in phenotypic diversity and can influence disease progression, drug responses, and environmental stress adaptation. Because of their potential to identify genes linked to significant biological traits and diseases, SNP profiling is immensely valuable in fields such as selective breeding, agricultural productivity, personalized medicine, and drug treatment.

What is SNP Genotyping?

SNP genotyping is the process of determining SNP loci on a genome-wide scale or within specific genomic regions. Its primary applications lie in disease management and pharmacogenomics. The genotyping can be categorized based on research objectives: Whole Genome Association and fine mapping. Common platforms used for SNP genotyping include SNP microarrays, Tokman SNP genotyping, MassArray SNP genotyping, and next generation sequencing (NGS).

SNP Genotyping Technologies and Platforms

With rapid advancements in SNP genotyping technologies, numerous public databases like BDSNP and Ensemble have emerged, accumulating identified SNPs. The major commercially available platforms for SNP genotyping are Affymetrix and Illumina arrays. These platforms are known for their reliability in various applications, including precision medicine, agricultural genotyping, forensic analysis, population-scale studies, and genome-wide association studies. High-density SNP chips cover most of the human genome and key plant and animal genomes. Both Affymetrix and Illumina systems utilize distinct principles for SNP detection, utilizing probes for both alleles and measuring binding signal differences to determine genotype.

Tokman SNP Genotyping

Tokman SNP genotyping provides a straightforward approach to SNP analysis. It features over 17 million pre-designed collections for various real-time PCR formats. Users can also create custom assays using the Tokman assay design tool. Each collection contains two allele-specific Tok Man MGB probes labeled with different fluorescent dyes alongside a complementary PCR primer pair, ensuring specific attachment to target DNA. The fluorescent method involves a five-prime end reporter dye and a three-prime quencher dye, where fluorescence is suppressed until exonuclease activity during PCR extension allows for dye release and subsequent signal measurement for genotype determination.

Mass Array SNP Genotyping

Mass array SNP genotyping allows multiple SNP analyses in a single reaction, offering improved accuracy and cost-efficiency when examining numerous SNPs. The approach uses a single extension primer, which facilitates allele-specific product generation across multiple PCR sites. Bonded with mass-modified dideoxynucleotide terminators, the PCR process involves an initial locus-specific primer followed by single base extension. The completed product's mass is analyzed using MALDI TOF mass spectrometry, offering an efficient and scalable SNP genotyping solution.