Despite the fact that the world is at the rapid phase of agricultural modernization, but we are still concerned about food security. To meet the demand of exponential increase in population there is requirement of 70% more food by 2050. To overcome this situation we have to improve our existing crop varieties and make them genetically diverse, adaptive to climate change, input use efficient, high yielding, enhanced nutritional attributes, and better adaptable to a wide range of agro-ecosystems and should not deteriorate existing environment. Among the various methods of breeding to improve crop varieties mutation breeding (induced mutation) plays a crucial role for the development of genetic variation among themselves. Over past five decade mutation breeding is getting more popular and till now 3,362 mutant plant varieties from 240 different plant species in more than 75 countries are released. Different types of physical, chemical and combined mutagens have been used by various breeder to induce genetic variability in various crops. 2635 varieties are developed by physical mutagens, 398 varieties are developed by chemical mutagens and 37 varieties are developed by combination of physical and chemical mutagens. Continent wise, 82 varieties are developed by Africa, 2049 by Asia, 10 by Australia and Pacific, 959 by Europe, 53 by Latin America, and 209 by North America. Similarly, 1602 major cereals, 501 major legumes and 86 major oil seed mutant crop varieties are developed by mutation breeding/induced mutation. Mutation breeding improve several qualitative and quantitative characters of crop plant and is successfully applied in several cereal, grain legume, oil seed, vegetable, fruits, medicinal plant, ornamental plants and fodder crops. With the advancement of various plant breeding, genetics, and biotechnological tools mutation breeding contribute toward the increase in global food and agriculture production which ultimately overcome global hunger and improve the nutritional status of the globe.

Heritable changes in the plant's phenotype are attributed to genomic sequence change and also by epigenetic variations. These epigenetic variations are involved in controlling plants' developmental processes. Intense and close breeding has reduced the genetic variations in crop increasing their susceptibility to the changing environment. Epigenetic diversity has now emerged as a new source of variation for coping with changing environmental stresses in plants. Epigenetic modifications like DNA methylation, post-translational histone modifications, histone variants, and involvement of non-coding RNAs have played a major role in gene expression and regulation in plants. These epigenetic modifications have created the variability in phenotypic expression by selective turning on and turning off of the genomic sequence. These variabilities are created in plants in response to the environmental factors to which plants are exposed. These phenotypic variations accumulated by epigenetic modification are transferred and expressed in the next generation as they are heritable. DNA methylation and methylation of histone tails on the lysine 4, 9, and 27 positions are among the best-characterized epigenetic marks observed in both plants and animals. These modifications marks have altered the physical state of the DNA. The alternation in the physical state of DNA has changed the way cell reads the genes. This is the potential new area of the research as it creates phenotypic variability in response to stress factors without changing the chemical properties of the DNA. In this paper, we have presented the epigenetic modifications and the way they controlled the gene expression in plants and animals.

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