A fusion gene is a hybrid gene that results from the fusion (usually reciprocal chromosomal translocation, e.g. through crossing-over between two sister chromatids) of two previously individual genes. Fusion genes can result from gene mutation or they can be developed artificially for research purposes.
A typical example is the BCR-ABL gene after exchange of genetic material between chromosomes 9 and 22 in chronic myeloid leukaemia (C92.10). Here the reciprocal translocation t(9;22)(q34;q11) is found. The fusion gene encodes the synthesis of a fusion protein with tyrosinase activity and proliferation-promoting and apoptosis-inhibiting activity.