Genomics At A Glance (I) : Molecular Markers & Genome Mapping

Genetic marker is any trait representing genetic differences between individual organisms or species. Generally, they do not represent the target genes themselves but act as 'signs' or 'flags'. Genetic markers that are located in close proximity to genes may be referred to as gene 'tags'. Such markers themselves do not affect the phenotype of the trait of interest because they are located only near or 'linked' to genes controlling the trait. All genetic markers occupy specific genomic positions within chromosomes(like genes) called 'loci'.There are three major types of genetic markers: morphological(also 'classical' or 'visible') markers which themselves are phenotypic traits; biochemical markers, which include allelic variants of enzymes called isozymes; and DNA(or molecular) markers, which reveal sites of variation in DNA.DNA-based markers offer several advantages over traditional phenotypic and biochemical markers. DNA-based markers are less affected by age, physiological condition of samples and environmental factors. DNA -based molecular markers have acted as versatile tools have found their own position in various fields like taxonomy, physiology, embryology,etc.