Animals
Segmentation in animals typically falls into three types characteristic of the different phyla: Arthropoda, Vertebrata, and Annelida. The three will be discussed here in using an example from each phyla, drosophila, zebrafish, and leech, respectively. Drosophila form segments from a field of equivalent cells based on transcription factor gradients. Zebrafish, and other vertebrates, use oscillating gene expression to define segments known as somites. Leech embryos, and other annelids, use smaller cells budded off from teloblast cells to define segments.
Read more about this topic: Segmentation (biology)
Famous quotes containing the word animals:
“Only the most acute and active animals are capable of boredom.—A theme for a great poet would be God’s boredom on the seventh day of creation.”
—Friedrich Nietzsche (1844–1900)
“Researchers, with science as their authority, will be able to cut [animals] up, alive, into small pieces, drop them from a great height to see if they are shattered by the fall, or deprive them of sleep for sixteen days and nights continuously for the purposes of an iniquitous monograph.... “Animal trust, undeserved faith, when at last will you turn away from us? Shall we never tire of deceiving, betraying, tormenting animals before they cease to trust us?””
—Colette [Sidonie Gabrielle Colette] (1873–1954)
“For the time of towns is tolled from the world by funereal chimes, but in nature the universal hours are counted by succeeding tribes of animals and plants, and by growth of joy on joy.”
—Ralph Waldo Emerson (1803–1882)