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Gene polymorphisms can occur in any region of the genome. The majority of polymorphisms are silent, meaning they do not alter the function or expression of a gene. [3] Some polymorphisms are visible. For example, in dogs the E locus can have any of five different alleles, known as E, E m, E g, E h, and e. [4]
Since all polymorphism has a genetic basis, genetic polymorphism has a particular meaning: Genetic polymorphism is the simultaneous occurrence in the same locality of two or more discontinuous forms in such proportions that the rarest of them cannot be maintained just by recurrent mutation or immigration, originally defined by Ford (1940).
An example of a botanical genetic polymorphism is heterostyly, in which flowers occur in different forms with different arrangements of the pistils and the stamens. The system is called heteromorphic self-incompatibility, and the general 'strategy' of stamens separated from pistils is known as herkogamy.
An example would be a seemingly silent mutation in the multidrug resistance gene 1 , which codes for a cellular membrane pump that expels drugs from the cell, can slow down translation and allow the peptide chain to fold into an unusual conformation, causing the mutant pump to be less functional (in MDR1 protein e.g. C1236T polymorphism changes ...
Genetic markers can be used to study the relationship between an inherited disease and its genetic cause (for example, a particular mutation of a gene that results in a defective protein). It is known that pieces of DNA that lie near each other on a chromosome tend to be inherited together.
Polymorphism can be maintained by selection favoring the heterozygote, and this mechanism is used to explain the occurrence of some kinds of genetic variability. A common example is the case where the heterozygote conveys both advantages and disadvantages, while both homozygotes convey a disadvantage.
For example, the standard protocols for DNA fingerprinting involve PCR analysis of panels of more than a dozen VNTRs. RFLP is still used in marker-assisted selection. Terminal restriction fragment length polymorphism (TRFLP or sometimes T-RFLP) is a technique initially developed for characterizing bacterial communities in mixed-species samples.
Incomplete lineage sorting (ILS) [1] [2] [3] (also referred to as hemiplasy, deep coalescence, retention of ancestral polymorphism, or trans-species polymorphism) is a phenomenon in evolutionary biology and population genetics that results in discordance between species and gene trees.