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:
“There is nothing worse than an idle hour, with no occupation offering. People who have many such hours are simply animals waiting docilely for death. We all come to that state soon or late. It is the curse of senility.”
—H.L. (Henry Lewis)
“Thou almost mak’st me waver in my faith
To hold opinion with Pythagoras,
That souls of animals infuse themselves
Into the trunks of men.”
—William Shakespeare (1564–1616)
“The alcoholic trance is not just a haze, as though the eyes were also unshaven. It is not a mere buzzing in the ears, a dizziness or disturbance of balance. One arrives in the garden again, at nursery time, when the gentle animals are fed and in all the world there are only toys.”
—William Gass (b. 1924)