Epigenetics (from Ancient Greek επί/epi = 'upon', 'over', 'above' and γενετικός/genetikos = 'genitive' > γενεά/genea = 'generation' > γεννώ/geno = 'birth to' > γένεσις/genesis = 'origin') is the study, in the field of genetics, of cellular and physiological phenotypic trait variations that are caused by external or environmental factors that switch genes on and off and affect how cells read genes. Hence, epigenetic research seeks to describe dynamic alterations in the transcriptional potential of a cell. These alterations may or may not be heritable, although the use of the term "epigenetic" to describe processes that are not heritable is controversial. Unlike genetics based on changes to the DNA sequence (the genotype), the changes in gene expression or cellular phenotype of epigenetics have other causes, thus use of the prefix epi- (Greek: επί- over, outside of, around).