This worksheet includes and an image that compares a protostome to a deuterostome. How organism’s develop from blastula to gastrula into one of two groups is another topic that fits into this unit. Here, I give my AP biology students a brief overview of the animal kingdom and some basic biology regarding invertebrates and vertebrates. Phylogeny, though, is a topic that will come up in any basic evolution unit. Nowadays, the idea is accepted by the majority of scientists as it has been confirmed by molecular data.Most advanced biology classes won’t go into great deal on individual groups within the animal kingdom. Many people regarded the idea that deuterostomes developed from ancient Bilateria through the conversion of the axis as extremely heretical. In deuterostomes (for example amphioxus or vertebrates) it is exactly the opposite: the central nerve cord is located on the dorsal side of the intestine, while the heart and the major blood vessels are located on the ventral side of the intestine. The blood is pumped from the heart, which is located on the dorsal side of the intestine, through a main artery, which is also located on the dorsal side. In protostomes (for example in Drosophila or earthworms) the central nervous system is located on the ventral side of the intestine. They concluded that the body axis must have been inversed not long after the evolutionary lineages separated from a common ancestor (“Nature“ 371: 26, 1994 “Development“ 126: 2309-2325, 1999). ![]() Katharina Nübler-Jung (from Freiburg), published a short paper in which they showed that the two genes had similar functions, albeit in opposing body regions. In 1994, Detlev Arendt, then a PhD student at the Institute of Zoology in Freiburg (now head of a group of researchers at EMBL in Heidelberg), and Dr. Apparently, a clear and undisguised view was required. ![]() (Photo: EMBL)Īlthough a homologue of dpp, bmp-4, was found and cloned in frog embryos, scientists did not find a parallel between insect morphogenesis and vertebrate embryos. Detlev Arendt, European Molecular Biology Laboratory in Heidelberg. ![]() In the amphioxus lancelet (Branchiostoma lanceolatum), a primitive deuterostome regarded as a model of the ancestors of vertebrates, there are 10 Hox genes, mice and humans have 38 arranged in four clusters that developed through duplication. Scientists found that the same homologous gene cassette also occurs in other animals, although the number of Hox genes varies. It is slightly confusing that these segments do not correspond with the developing segments of the fly. Each of the genes is expressed in particular body segments. Drosophila has eight Hox genes that are arranged in linear order on the chromosome. The proteins encoded by the Hox genes either directly or indirectly control the transcription of numerous genes, including those that are responsible for the formation of typical features in the individual embryo segments. The Hox genes were initially discovered in Drosophila and have a typical sequence of approximately 180 base pairs (homeobox), which encode a particular DNA-binding region. One of the most important discoveries of modern evo-devo research (evolution plus development) is that the embryonic longitudinal axis in animals develops according to the same principle, i.e. Conserved genes during embryonic development ![]() They differ from other phyla because they shed their skin (Greek: Ecdysis) during individual development. The arthropods (insects, crayfish, spiders, centipedes, etc.) and other relatives are nowadays grouped as Ecdysozoa together with the unsegmented nematodes (ring worms like for example the favourite experimental animal of molecular biologists, Caenorhabditis elegans). This classification can be seen as a late triumph for the classical developmental biologists or embryologists, who suggested a big similarity between Trochophora larvae and marine annelids and snails. Nowadays, they are grouped as Lophotrochozoa, together with molluscs. Previously, scientists thought that annelids (bristle worms) were related to arthropods due to their segmentation. In terms of the division of major phyla, the molecular data suggest some radical changes. Of course, there were also some new views: A few invisible candidates – such as Brachiopoda and Bryozoa – which were often regarded as deuterostomes, now count as protostomes. It was possible to confirm this basic division of the animal kingdom into protostomes and deuterostomes by modern analyses used in molecular phylogeny.
0 Comments
Leave a Reply. |