Maize (Zea mays ssp. mays) is known to have been domesticated in the lowlands of Southwest Central Mexico, precisely in Balsas Valley from a single progenitor wild grass, teosinte (Zea mays spp. parviglumis) about 9000–10,000 years ago. However, the success of present-day maize is attributed to the mixed origin of maize as two teosinte species, namely Zea mays ssp. parviglumis and Zea mays ssp. mexicana, have contributed to the maize genome. In addition, selection by early indigenous humans has also played a vital role in making modern-day maize plants (longer ears with more kernel rows) from wild grass teosinte. Presently, maize has attained the status of an important cereal crop with the highest production (1163 million MT) and productivity (5718 kg/ha) in the world. It is cultivated in >170 countries in the world across diverse ecologies viz., lowland, midland, highland in tropica, sub-tropics, and temperate regions from mean sea level to 3600 metre above sea level (masl). It is widely used for animal feed and biofuel production in the world. Further, it is also used as a raw material in starch and food processing industries. The maize starch is extensively used in several industries like pharmaceuticals, textiles, confectionaries, etc. Maize is classified into different types based on grain texture (flint, dent, semi-dent/ semi-flint), special uses or biochemical composition (sweet corn, popcorn, waxy maize, high amylose maize, high-oil maize, baby corn), and nutritional value (quality protein maize, high-methionine, biofortified maize). The above versatility in its adaptation, uses, and types reflects the underlying genetic diversity present in the maize. The genetic diversity in the maze is the reflection of underlying allelic variations of a gene and/or across different genetic loci in the maize genome. Maize, being a highly cross-pollinated crop, harbours a large number of spontaneous recessive mutations in the natural populations and is maintained in heterozygous conditions. Nonetheless, small proportions of recessive mutations are exposed to natural as well as human selection. The mutant phenotypes are also used as morphological markers for the indirect selection of traits of interest as well as various genetic studies. Gregor Johann Mendel from Austria, the father of genetics, was the first botanist who used maize to study the applicability of principles of inheritance he observed in Pisum (garden pea). Later, two other botanists, namely Carl Erich Correns of Germany (German) and Hugo Marie de Vries of the Netherlands (Dutch), also used maize to study the inheritance pattern, who rediscovered Mendel’s Laws of Inheritance along with Erich von Tschermak. The genetic studies on anthocyanin colour types placed maize genetics on firm footing to further undertake various genetic studies by several geneticists to bring more insights into the general applicability of Mendel’s Laws of Inheritance. Subsequently, efforts were made to unravel the physical nature of genetic factors. The successful identification of each of the ten chromosomes of maize, assigning linkage groups to individual chromosomes, and description of each chromosome in terms of total length, arm ratios, and position of heterochromatic regions have led to the birth of a new discipline, the cytogenetics. Later, development of biometric models has been developed to estimate the approximate number of genes involved in determining the traits. In the 1950s, the structure of genetic material, the deoxyribose nucleic acid (DNA), opened new avenues to understand the physical nature of gene(s) resulting in the birth of molecular genetics, another subsidiary of genetics. Later development of DNA sequencing technologies followed by an effort to edit specific gene(s) or DNA sequences to bring desired changes in the phenotype of interest or correct the specific defects in the gene(s) or trait(s) led to site-specific directed mutagenesis or editing specific sequences in the genome. As a result, it has opened up infinite avenues to bring desired changes in the genotype. However, the germplasm is vital for any advances in either genetics or plant breeding. In this regard, effective identification of desired germplasm is crucial in the maize breeding programmes. Mass selection of desirable maize ear and grain type during the early nineteenth century was one of the most primitive breeding methods. However, inbreeding through generations of self-pollination followed by outbreeding led to the advent of hybrid breeding or heterosis breeding. Hybrid breeding is one of the most revolutionary breeding methods in the history of agriculture which has led to enhancement in maize yield by many folds. In order to make use of heterosis phenomenon in hybrid development/breeding, it is of prime importance to identify inbred lines which are heterotic to each other. Several methods have been developed since the advent of hybrid breeding/heterosis phenomena to classify inbred lines into different heterotic groups based on the combining ability or identify heterotic pattern. Assigning inbred lines to distinct heterotic groups is fundamental to maximize exploitation of heterosis.