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A molecular marker, also referred to as a genetic marker, is a particular sequence of deoxyribonucleic acid, or DNA, that is identifiable within the context of an entire genome. Researchers use molecular markers to keep track of the locations of particular genes or other noteworthy DNA sequences within a larger strand of DNA. Some molecular markers can only be identified by examining the sequence of genetic information while others can be identified by visual examination of an organism. These markers serve many purposes in biological research, including those of an academic nature and those that are more therapeutic. Academic applications might involve cataloging genes that affect particular traits while therapeutic applications involve researching markers to help identify genetic variations in the hopes of treating disease.
There are many different types of molecular markers of varying lengths and configurations that can be used for many different purposes. Some occur naturally while others are specifically developed by researchers to mark the positions of certain DNA sequences. Various laboratory processes can be used to add molecular markers to particular DNA sequences or to splice DNA strands at points indicated by the presence of molecular markers. Applying some techniques based on such markers allows researchers to make "genetic maps" containing a given organism's coded genetic information.
Molecular markers must possess a few distinct traits in order to be useful to researchers. For instance, they must be easy to locate and identify with certainty, as any doubt could call final results of experiments based on markers into question. They must also be polymorphic, meaning that different forms of the gene coded by the marker exist in different organisms of the same species and result in some form of change in the organisms. In general, there is little information to be gained from non-polymorphic sites. Also, polymorphisms lead to visible changes, such as eye color or wing structure, that can be used to identify which organisms have which particular genetic makeup.
Various processes in biological research use molecular markers for a wide range of purposes. They are commonly used to try to determine how specific physical traits or conditions are linked to genetic variables. Sometimes, this is done for purely academic purposes, as researchers are often interested in determining which genes affect which physical traits. It can also be used for therapeutic purposes, though. Some genetic variations, for instance, can lead to disease, so investigating variations in polymorphic molecular markers may lead researchers to some insight about the nature of genetic diseases.