Genetic Polymorphisms – Classification, Structure, Detection and Function

Human genome represents the entire DNA present in a viable human cell put together that contains all the information required to guide numerous life-sustaining cellular processes. The Human Genome Project (HGP) was undertaken mainly with the aim of establishing a reference genome deciphering, in detail, the basic structure, organization and function of all the genes present in the human genome, including the instructions required for the growth, development, function and survival of human beings. The HGP also revealed the highly conserved nature of human genome because of which all the humans share at least 99.5% sequence similarity and exhibit only a difference of around 0.1%–0.5%. This small difference between different genomes along with epigenetic modifications determines almost all the phenotypic diversity or differences that exist between any two individuals within and/or between populations. The genetic variations represent the variability that occurs in a human genome in comparison with other genomes and the reference genome established by the HGP. These genetic variations include two main types: the more commonly occurring genetic variations termed as genetic polymorphisms and the rare, less commonly occurring and often disease-causing genetic variations termed as mutations. Genetic polymorphism represents the most dynamic and most common form of genetic variations that occur in the human genome. It includes several major types of annotated genetic variations such as single nucleotide polymorphisms (SNPs),small indels, variable number of tandem repeats (VNTRs),short tandem repeats (STRs),copy number variations (CNVs; deletions or duplications),copy neutral variations (inversions and translocations) and transposable (mobile) element insertions. Genetic polymorphisms can directly lead to or may influence the phenotypic variations, including the difference in traits such as height; color of eyes, hair, and skin; and, and response to pathogens, chemicals, drugs and vaccines, and may modulate the susceptibility to or even cause various diseases including genetic disorders and multifactorial diseases. The methods or techniques used for the detection, analysis and characterization of genetic polymorphisms are diverse and dynamic. These techniques include several traditional techniques and their modifications that allow low- to medium-throughput detection and analysis and several other techniques including the new and emerging techniques such as next-generation sequencing (NGS)-based techniques that enable high-throughput detection and analysis of genetic variations.