Chapter 6 Web links and web activities

Development of nematodes and sea urchins

The nematode C. elegans is a relatively recent addition to the pantheon of model organisms, having been developed as an experimental system during the 1970s. One of its most attractive features was its invariant cell lineage: from the time the egg is fertilized, each cell's fate is known. This promised the opportunity to correlate genes, gene expression patterns, and cell-cell interactions with specification and determination at a level of resolution unavailable in any other organism. One of the important findings from this lineage work was that C. elegans, and organisms in general, make many more cells than they need, then get rid of the extra cells by programmed cell death, or apoptosis. The powerful genetics of C. elegans allowed the genes required for cell death (the "ced" genes) to be identified. The importance of the human counterparts to these same genes for understanding human cancer led to a Nobel Prize in 2002 for this work ( To learn more about the explorations into cell death during C. elegans development from one of the pioneers in the field, go to:, contains resources for the biology and genome of Caenorhabditis elegans. is a database of behavioral and structural anatomy of Caenorhabditis elegans. and
The Sea Urchin Embryology and the Virtual Urchin websites from Stanford University provide a variety of laboratory resources for students, including ideas for experimentation and a series of “virtual labs”. 
View the animations and videos to answer the following questions:

  • What happens when two or more sperm make it into the egg?
  • How does the female pronucleus behave before fusing with the male pronucleus?

You might like to also refer to Chapter 9 where this topic is discussed in detail.    
For a genomic and developmental tour of the ascidian Ciona intestinalis visit the Chordate Neural Development laboratory of Jean-Stephane Joly in France, where you will find a link to FABA, the Four-Dimensional Ascidian Body Atlas. Compare the developmental time table to the other model organisms studied and view the interactive cell lineage demonstration. From the information found in the atlas determine the characteristics of the notochord during development of Ciona.