Molecular markers in crop improvement
Authors: Sundeep Kumar, Amit K. Singh, Ruchi Bansal, Sheel Yadav, Jyoti Kumari and Rakesh Singh
National Bureau of Plant Genetic Resources, New Delhi

Molecular markers are segment of DNA sequence of the genome that can differentiate two or more individuals/genotypes and follow the Mendelian pattern of inheritance. Molecular markers have been introduced over last two decades, which has revolutionized the entire scenario of biological sciences. Since the publication of restriction fragment length polymorphism (RFLP); first DNA marker techniques three decades ago, many DNA based marker techniques have been developed which includes RAPD, SSR, ISSR, CAPs etc. DNA based markers have found large scale applications in crop improvement programs, because of several advantages over morphological and biochemical markers. Molecular markers are environmentally neutral, highly abundant, and independent of tissue and stage of the plants. Traditionally, breeders have relied on visible traits to select improved varieties however; MAS rely on identifying marker DNA sequences that are inherited alongside a desired trait during the first few generations. Molecular markers are also considered as useful tools for pyramiding of different resistance genes and developing multi-line cultivars targeting for durable resistance to the disease. Although there is no marker technique which is without any limitation but an ideal molecular marker should have following features: 1) technically simple and easy to perform 2) follow co-dominant inheritance 3) require no prior sequence information about genome 4) reproducible and 5) generate more number markers per reaction

However, most of the currently used molecular markers are random DNA markers (RDMs) derived from unknown regions of the genome, limiting their use in trait specific crop improvements. Therefore, the focus in the recent years has been to develop markers which are derived from the within the gene regions making them more useful for crop improvement per se. These markers are referred as gene targeted markers (GTMs). And those gene targeted markers which are derived from the polymorphic site within the genes having effect on phenotypes of the plants are referred as functional markers (FMs).

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About Author / Additional Info:
Currently, I am working as Senior Scientist at National Bureau of Plant Genetic Resources, Pusa, New Delhi-110012 (INDIA).