Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 3, page 1Lecture 3: Model Systems and their features Text: 2nd Ed.:31; 36; 42; 49; 52; 191-192; 201-212. 3rd Ed.:186-188; 32; 203; 4-5; 97; 100; 105. Some figures in these notes are redrawn or reproduced from Wolpert et al. (2nd and 3rd editions). Our working ‘Tree of Life’ – a phylogeny of animals (We will be talking more about this phylogeny in the lecture on evolution and development.) The bilateriaare the bilaterally symmetrical animals with three germ layers (triploblasts), as opposed to the radiata(radially symmetric comb jellies and jellyfish, which are diploblasts) and sponges. For some groups, the bilateral symmetry refers to the larval form. The last common ancestor of the bilateria is believed to have existed some 540 million years ago. Model Systems It is impossible to get a complete picture of the development of all animals, of course, but it is through the study of representative model systemsthat we seek to understand strategies that various systems use. We hope to learn what features are universal, as well as what features are specific to particular systems. Ultimately, developmental biologists are interested in how developmental mechanisms have evolved over time. One of the central principles of evolutionary biology is that all animals are related by common descent: Similar animals have a more recent common ancestor than more divergent animals. For example, the development of fish is more similar to that of mouse than it is to Drosophila. Another important principle is that thechanges in development and form emerge from changes at the level of genes. In the past two decades, molecular techniques have allowed us to probe development at the most fundamental level, and perhaps the most gratifying finding has been that even very diverse animals use similar strategies to solve particular problems. For example, we’re going to see that one set of genes, the Hox genes, forms a genetic toolkit that different animals have co-opted over time to specify differences along a spatial axis. Here we will take a brief look at these species and indicate the advantages that they have for analysis of development. In the course we will examine the development of C. elegans, Drosophilaand Xenopus in the most detail. First, we will define the features of the three main modes of cell type specification.
has intentionally blurred sections.
Sign up to view the full version.