What is Gene expression?
'''Gene expression''' is how the information in a [[gene]] (the sequence of [[DNA]] base pairs) is made into a [[Product (chemistry)|product]] (such as a [[protein]] or [[RNA]]). The basic idea is that DNA is [[Transcription (genetics)|transcribed]] into RNA, which is then [[Translation (genetics)|translated]] into proteins. Proteins make many of the structures and all the [[enzyme]]s in a [[Cell (biology)|cell]] or [[organism]]. [[File:Gene expression control.png|thumb|right|300px|Diagram showing at which stages in the DNA-mRNA-protein pathway expression can be controlled]] Several steps in gene expression may be tuned. This includes both the transcription and translation stages, and the final folded state of a protein. Gene regulation switches genes on and off, and so controls [[cell differentiation]], and [[morphogenesis]]. Gene regulation may also serve as a basis for evolutionary change: control of the timing, location, and amount of gene expression can have a profound effect on the development of the organism. The expression of a gene may vary a lot in different tissues. That is how the tissues become different from each other. This is called [[pleiotropism]]. This term is important in [[genetics]]. == Epigenetics == In [[biology]], [[epigenetics]] is the study of [[Heredity|inherited]] changes in [[phenotype]] (appearance). Gene expression can be adjusted in ways other than the underlying [[DNA]] sequence. These changes may remain through [[cell (biology)|cell]] [[mitosis|division]]s for the remainder of the individual's life, and may also last for more than one generation. However, ''there is no change in the underlying DNA sequence of the organism''.<ref>{{cite journal| title=Perceptions of epigenetics| author=Adrian Bird| journal=Nature| volume=447| pages=396–398| year=2007| issue=7143| doi=10.1038/nature05913| pmid=17522671| bibcode=2007Natur.447..396B| s2cid=4357965}} PMID 17522671</ref> Instead, non-genetic factors cause the organism's genes to behave (express themselves) differently.<ref>{{Cit