It is a term used in genetics to describe multiple forms of a single gene that exists in an individual or among a group of individuals.
The word is a combination of the Greek words poly (which means multiple) and morph (form of meaning).
Polymorphism and genetics
Where monomorphism means having only one form and dimorphism means that there are only two forms, the term polymorphism is a very specific term in genetics and biology, related to the multiple forms of a gene that can exist.
The term does not extend to character traits with continuous variation, such as height (although this may be an inheritable aspect). In contrast, polymorphism refers to forms that are discontinuous (have discrete variation), bimodal (that have or imply two modes) or polymodal (multiple modes).
For example, the lobes of the ears are attached, or not, it is any situation and not as the height, which is not an established number or another.
Polymorphism was originally used to describe visible forms of genes, but now the term is used to include cryptic modes, such as blood types, that require a blood test to decipher.
In addition, the term is sometimes incorrectly used to describe visibly different races or geographical variants, but polymorphism refers to the fact that multiple forms of a single gene must occupy the same habitat at the same time (which excludes geographic, racial morphs). or seasonal).
Genetic polymorphism refers to the appearance of two or more genetically determined phenotypes in a given population (in proportions that the rarest characteristics can not be maintained only by recurrent mutation).
Polymorphism promotes diversity and persists over many generations because no single form has a general advantage or disadvantage over others in terms of natural selection.
Uses of polymorphisms
Genetic polymorphisms, whether studied in the form of allozymes, RFLP, microsatellite or microsatellite variation, or DNA sequences, have become useful tools in a variety of research fields such as population genetics, evolutionary genetics, systematics, and molecular phylogeny , human genetics, genetic and forensic agriculture.
Genetic polymorphisms, through multiple alleles at individual loci, provide a mechanism for labeling a gene or piece of DNA, which is a powerful tool for a variety of investigations.
Some of these investigations are the identification of genotypes in paternity and forensic studies, movement of individuals in field studies, progress of selection experiments in populations, quantitative affecting economic traits in plants and animals, mapping of disease genes in Human and evolutionary comparisons of DNA sequences.
The uses of genetic polymorphisms are almost infinite. In a period of only 50 years, our image of genetic variation in natural populations has moved from almost monomorphism to ubiquitous polymorphism in all organisms whose populations have not gone through severe bottlenecks in their recent evolutionary history.
Is it the same as a mutation?
Mutations by themselves are not classified as polymorphisms. A polymorphism is a variation of DNA sequence that is common in the population.
A mutation, on the other hand, is any change in an abnormal DNA sequence (which implies that there is a normal allele that crosses the population and that the mutation changes this normal allele to a rare and abnormal variant).
In polymorphisms, there are two or more equally acceptable alternatives and to be classified as a polymorphism, the least common allele must have a frequency of 1% or more in the population. If the frequency is less than this, the allele is considered a mutation.
Polymorphism and Enzymes
Gene sequencing studies, such as the one done for the human genome project, have revealed that at the nucleotide level, the gene that codes for a specific protein can have several differences in sequence.
These differences do not alter the overall product significantly to produce a different protein but may have an effect of substrate specificity and specific activity (for enzymes), binding efficiencies (for transcription factors, membrane proteins, etc.) or other characteristics and functions.
For example, within the human race, there are many different polymorphisms of CYP 1A1, one of the many liver enzymes of cytochrome.
Although enzymes are basically the same sequence and structure, polymorphisms in this enzyme can influence how humans metabolize drugs.
CYP 1A1 polymorphisms in humans, where, in exon 7, the amino acid Isoleucine is replaced by Valine, it has been linked to lung cancer related to smoking.
The use of genetic polymorphisms was one of the strengths of deCODE Genetics, a company that focused on determining genetic risk factors for various diseases.