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)
“The saying, “The Magyar is much too lazy to be bored,” is worth thinking about. Only the most subtle 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)
“In their sympathies, children feel nearer animals than adults. They frolic with animals, caress them, share with them feelings neither has words for. Have they ever stroked any adult with the love they bestow on a cat? Hugged any grownup with the ecstasy they feel when clasping a puppy?”
—Jessamyn West (1907–1984)