This is a mechanism used by the lymphocytes of vertebrates to produce millions of different antibodies. It is also a mechanism used by yeast cells to control mating. Certain genes are selectively activated in specific tissues in response to developmental and environmental signals. DNA sequences that regulate transcription of gene in response to specific signals have been identified in the transcriptional start sites of various eukaryotic genes and are called response elements . Heat shock response elements are those DNA sequences that bind heat shock proteins.
Homeotic genes regulate embryonic development by coding for transcription factors.