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DNA marker is a new approach based on DNA polymorphism among tested genotypes, (John and Williams, 2008), thus, applicable to biological research. It offers many advantages over other categories of markers such as morphological, cytological or biochemical markers. For example, DNA marker can cover the whole genome and, therefore, is much larger in quantity. There is more polymorphism in DNA markers, which are able to reveal the variation and allelism. Many DNA markers are co-dominant and can differentiate between the homozygous and heterozygous genotypes. Furthermore, DNA markers are “neutral”, and they have no effect on phenotype, no epistatic effect, and are not influenced by environmental conditions and development stages. Therefore, DNA marker is simple, quick, less environmentally conditioned, and experimentally reproducible well. It has been applied widely in the identification, registration of plant variety, and in monitoring of the seed purity and the authenticity with high accuracy, high reliability and low cost. However, due to rapid developments in marker technology, statistical methodology for identifying quantitative trait loci (QTLs) and the jargon used by molecular biologists, the utility of DNA markers in plant breeding may not be clearly understood by non-molecular biologists. This review provides an introduction to DNA markers and the concept of polymorphism, linkage analysis and map construction, the principles of QTL analysis and how markers may be applied in breeding programs using MAS.
