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Genetic polymorphism studies in humans

Genetic polymorphism is defined as the inheritance of a trait controlled by a single genetic locus with two alleles, in which the least common allele has a frequency of about 1% or greater. Genetic polymorphism is a difference in DNA sequence among individuals, groups, or populations. Sources include single nucleotide polymorphisms (SNPs), sequence repeats, insertions, deletions, and recombination. Genetic polymorphisms may be the result of chance processes or may have been induced by external agents such as viruses or radiation. If a difference in DNA sequence among individuals has been shown to be associated with disease, it will usually be called a genetic mutation. Changes in DNA sequence that have been confirmed to be caused by external agents are also generally called ‘mutations’ rather than ‘polymorphisms’. SNPs are the most common type of genetic variations in humans. Understanding the functions of SNPs can greatly help us understand the genetics of human phenotype variation, especially the genetic basis of complex human diseases. DNA polymorphisms comprise three types: tandem repeat polymorphism, copy-number variations and SNPs. Detection of these polymorphisms can be carried out by different methods including allele-specific PCR, restriction fragment length polymorphism, the microarray technique, and whole genome sequencing. Calculation of the sample size is very important in studying any polymorphism using specific free software. Here we shed some light on DNA polymorphisms and their implications as genetic markers in polygenic diseases.