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:
“I wish more and more that health were studied half as much as disease is. Why, with all the endowment of research against cancer is no study made of those who are free from cancer? Why not inquire what foods they eat, what habits of body and mind they cultivate? And why never study animals in health and natural surroundings? why always sickened and in an environment of strangeness and artificiality?”
—Sarah N. Cleghorn (1976–1959)
“Of all the animals with which this globe is peopled, there is none towards whom nature seems, at first sight, to have exercised more cruelty than towards man, in the numberless wants and necessities with which she has loaded him, and in the slender means which she affords to the relieving these necessities.”
—David Hume (1711–1776)
“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)