John Sulston who determined the cell lineage of ALL THE CELLS in the model organism Caenorhabditis elegans (male and female) has died at the age of 75. He shared a Nobel prize for this work. The C. elegans worm is about 1 mm long and has (not counting eggs and sperm) exactly adult 959 cells in hermaphrodites and adult 1031 cells in the male animal has a mutation affecting these things or its. These are exact numbers unless the animal is damaged or has a mutation affecting these things. Sulston discovered that the lineages generating the individual adult cells are almost entirely invariant, the same cell precursor cell always making the same result after division. This has made C. elegans great for doing research in its development since you can always be sure of observing the same cell in a number of different organisms. Although the lineages are almost invariant, studies have shown that the cells resulting from some of the divisions are determined by cell-cell interactions rather than strictly by a lineage determined mechanism. The invariance of development in this small developing organism is explained by its very constrained developmental environment (which cells are next to which other cells is very reproducible). He also worked in the human genome project at the Sanger Institute and promoted open access for research papers.