Variation in DNA, and genes to a lesser or greater extent, can play an important role in most diseases; that is because this variation in will reflect and affect the function of DNA, and genes (combined genes and DNA or separately). This can be affected by environment, life style, as well as the inheriting from parents and previous generations. All these factors can contribute in human diseases. There are different alterations in genes, like imbalance and inequality in chromosomes, disorder in gene (deficiency in gene, which could be complex or single disorder), and cancer. In the last decades, scientists were focus on medicine and genetics; they pay an extensive attention to reach better understanding about diseases and their causes, to serve patients in better way. This tendency and preparations were focused on genes and the changes that may occur, and the sequences of these changes on health. In this regard scientists studied the epigenetic diseases as well, and the application of genes in therapy. Implementation of these concepts in labs and clinics required full understanding of genetic alterations.