Using Progenitor Cells and Gene Chips to Define Genetic Pathways

The zygote is a single cell, a fertilized egg, capable of giving rise to a complete organism. This is a truly remarkable transformation, with a single cell becoming trillions of cells or more, with a microscopic mass becoming in some cases tens or hundreds of kilograms, with a single amorphous cell making a number of complex organs, including the brain with its uncountable precise synaptic connections. For mammals, which generally appear to lack localized cytoplasmic determinants, this process is guided by a genetic program encoded in the DNA of the zygote.