Genes whose products are required for the timing of specific developmental events. Mutations in these genes disrupt the temporal pattern of development and can also lead to phylogenetic variation. In Caenorhabditis elegans mutations in single heterochronic genes affect the timing of cell division and differentiation in different post-embryonic cell lineages (without affecting other lineages), resulting in the generation of cell patterns normally associated with earlier or later developmental stages. Two of the heterochronic genes in C. elegans, lin-4 and let-7, encode small temporal RNAs (q.v.), which control developmental timing by inhibiting the translation of target messenger RNAs. Other heterochronic genes affect the timing of neuroblast proliferation (Drosophila), scale cell maturation (Papilio), sporulation (Dictyostelium), post-embryonic shoot development (maize), and flower formation (Arabidopsis). In many eukaryotes the timing of many developmental events is controlled by hormones, and numerous genes affecting hormone function have been described. However, little is known about what controls the timing of hormone secretion. See Chronology, 1984, Ambros and Horvitz; heterochrony.
Subjects: Genetics and Genomics.