**1. Introduction**

The genetic variability is something common to all the living organisms and has important implications for the evolution and conservation of every species. It is widely known the differences in the phenotype among individuals are strictly dependent on two factors: the genotype, which is inherited from our ancestors, and the surrounding environmental exposure that contributes to shape the phenotype. The interindividual and intraindividual genetic differences make humans special and unique determining for each a single identity. Although genetics influences our physical appearance, behaviour, thoughts and habits, we recognize also the environment plays a crucial role in modifying many other parameters of our body. This depends on several factors: the country where we live, the ethnicity to which we belong to, the historical heritage, tradition and religion, the interaction with other people as well as the influence of the climate change on our life. If, on the one hand, our genetic heritage makes us unique, we acknowledge that classic genetics cannot explain the wide diversity of phenotypes within the population; nor classic genetics can explain the different phenotypes and disease susceptibility found in identical twins as well as in organisms obtained by cloning technology despite the DNA being exactly the same [1]. That means we cannot forget the strong influence

of the surrounding environment on our genotype and on our physiological, physical and behavioral habits. Such influence, namely, epigenetics, means that the heritable changes in gene expression are not due to alteration in the DNA sequence but to some modifications occurring upon the DNA without changing the genetic code. That said, although we are aware the genetic variability is something peculiar to every human being, regardless of the inheritance of favorable or unfavorable genes, the transmission to the offspring will be modulated by epigenetics contributing to increase further the genetic variation in the population.
