text: Although ectopic expression can be caused by a natural condition, it is uncommonly seen in nature because it is a product of defects in gene regulation. In fact, ectopic expression is more commonly used for research purposes. Artificially induced gene expression helps to determine the function of a gene of interest. Common techniques such as overexpressing or misexpressing the genes by UAS-[http://flystocks.bio.indiana.edu/Browse/uas/uashome.htm Gal4] system in D. melanogaster are used. In model organisms, such techniques are used to perform genetic screens to identify a function of the gene involved in specific cellular or developmental processes.
  Ectopic expression using these techniques is a useful tool because phenotypes induced in a tissue or cell type where are not normally expressed are easily distinguishable compared to a tissue or cell type where the gene is normally expressed. By the comparison with its basal expression, the function of a gene of interest can be identified.
  Although the understanding of ectopic expressions deals with endogenous genes in an organism, it can be expended to a similar concept like transgenesis, which an exogenous gene is introduced to a cell or tissue type in which the gene is not usually expressed. Practices of ectopic expression in biological science is not only limited to identifying a function of the gene in a known cell or tissue type but also implemented to discover unknown or additional functions of the gene by ectopic expression.