……. Billions of dollars were spent to map the human genome because scientists hoped to find the genes responsible for diseases like cancer, heart disease, and stroke. This knowledge, they thought, would allow them to design specific drugs and maybe even find a way to replace defective genes. For decades, we assumed that the Human Genome Project would reveal a hereditary basis for most diseases, just as they had been found for phenylketonuria, Huntington’s chorea, Duchenne muscular dystrophy, sickle cell anemia, and cystic fibrosis.
The first surprise of the project was the relatively small number of genes found in humans. Scientists found that we have fewer than many other animal and plant species, and we share at least 95 per cent with our nearest relatives, chimpanzees. We now assume the number of genes isn’t what distinguishes higher forms but the timing of gene actions and interactions.