Abstract: The present invention relates to cell death genes, which are genes required for programmed cell deaths; mutant organisms, in which embryonic programmed cell death occurs to a less than normal extent; proteins encoded by the cell death genes; antibodies which bind the cell death gene products; and agents which alter the ability of cell death genes to cause programmed death of cells. As described herein, Applicants have identified two genes which function in the initiation of apoptosis or programmed cell death. These two genes, referred to respectively as the reaper (rpr) gene and the head involution defective (hid) gene, map to position 75C1,2 on the third chromosome in Drosophila (D.) melanogaster and, as described in detail below, exhibit expression patterns related to the pattern of cell death during Drosophila embryogenesis; mutations in each gene reduce levels of cell deaths or abolish cell death.