Each of us carries up to 100 of the genes responsible for diseases such as cancer and diabetes, a new study has found.
According to a 'catalogue' of genetic faults compiled by scientists, we also have around 300 genes that are so flawed they don't work at all.
Hundreds of researchers from around the world, including British experts, have combined forces to analyse the tiny genetic differences between individuals.
The results will offer the deepest insight yet into the human genome, or genetic blueprint, and could shed new light on what makes us human.
And the 1,000 Genomes Project will also help scientists work out why some people are more susceptible to disease than others.
The study involved reading the DNA of more than 800 volunteers from around the world.
According to the results, on average, each individual has between 250 and 300 genes that are so flawed they don't work at all.
Each of us also has around 75 to 100 genes that are known to have links to inherited diseases.
In many cases, they will not cause any problems, with people carrying the disease but not becoming ill themselves.
But learning more about how they, and other flaws, trigger disease could lead to new drugs, genetic tests and even ways of preventing ill health.
The human genome is estimated to contain up to 25,000 genes in total.
"It is clear that disease is influenced by inheritance but also by environment, behaviour and by chance," the Daily Mail quoted Dr David Altshuler, of Massachusetts General Hospital in Boston in the U.S., as saying.
"Moreover it is clear that most diseases are influenced by many genes and by many variations in many genes. It is not a simple problem.
"Nonetheless we continue to drive towards using DNA technology to illuminate disease and we do this despite knowing each success is just the first step towards the biological investigation of that disease.
"The reason we do this is because we live in time when one of the great scientific opportunities is to use this new ability to read DNA in our population.
"We do believe in the long-run this is a very valuable and promising approach to learn new things about the basis of disease and if we do that as a field and then biological follow-up occurs this has promise to contribute to improvements in human health."
The results were published in the journals Nature and Science.