The word 'polymorphism' literally means 'a state of having many shapes' or 'the capacity to take on different forms'.
Polymorphism occurs when many different physical forms or types of individuals exist among the members of a species.
A discontinuous genetic variation divides the individuals of a population into two or more sharply distinct forms. The most obvious example of this is the separation of most higher organisms into male and female sexes. Another example is the different blood types in humans. In continuous variation, by contrast, the individuals do not fall into sharp classes but instead are almost invisible graded between wide extremes. Examples include the smooth graduation of height among individuals of human populations and the graduations possible between the different geographic races. If the frequency of two or more discontinuous forms within a species is too high to be explained by mutation, the variation as well as the population showing it, is said to be polymorphic. In polymorphisms, there are two or more equally acceptable alternatives. To be classified as a polymorphism, the least common allele must have a frequency of at least 1% in the population. If the frequency is lower than this, the allele is regarded as a mutation.
Different types of polymorphisms include:
Single nucleotide polymorphisms (SNPs)
Single nucleotide polymorphisms (SNPs), pronounced as snip, are an alteration in a DNA order structure building block units (A, T, C, or G) which are known as a nucleotide. It is the simplest formula of genetic difference among persons. SNPs are the most frequent occurrence from all genetic variants, which happen usually in a person’s DNA. It is a ratio of occurrence near 90% of human genomic variants.
They may be occurring one time in each 300 nucleotides on usual, that is, average is about 10 million SNPs in the individual’s genome. Greatest frequently, those SNPs are set between genes or within genes. They may perform as living signs or hereditary indicators, helping in experts finding sequence, which are linked with disease. However, the SNPs generally have no influence on the general state of health.
Variable number of tandem repeats (VNTRs)
It is a kind of tandem repetitions in which a small order of bases (10–60 base pairs) are frequented changeable times in a certain position. Therefore, VNTR is additionally familiar as minisatellites. Minisatellites are scattered everywhere in the humane DNA. Usually, the number of repeated bases in minisatellites differs among persons. Hence, the array extension shaped by VNTRs as well differs among persons.
Insertion/deletion polymorphisms
It is a type of genomic difference in which a particular base order of different sizes ranging from one base to many 100 units is inserted or deleted. Indels are very extending across the DNA.
Allelic polymorphism
It occurs when there are multiple alleles expressed within the population, alleles are different versions of a trait or physical characteristic. Examples include peppered moths, human blood groups, and two-spotted ladybugs.
Genetic polymorphisms
These are the concurrent occurrence of two or more discontinuous genotypes or alleles in a population. Genetic polymorphisms determine the diversity of individuals.
Simple sequence length polymorphism (SSLPs)
Simple Sequence Length Polymorphisms are used as genetic markers with polymerase chain reaction (PCR). An SSLP is a type of polymorphism that is a difference in DNA sequence amongst individuals.
Restriction Fragment Length Polymorphism (RFLP)
It is a difference in homologous DNA sequences that can be detected by the presence of fragments of different lengths after digestion of the DNA samples with specific restriction endonucleases. RFLP, as a molecular marker, is specific to a single clone/restriction enzyme combination.
DNA polymorphisms
The type of polymorphism that detect spelling variations at the level of DNA nucleotides.
