And remember that the natural substances we encounter can sometimes change a gene. Scientists say that some of our genes were modified by conditions hundreds of years ago and were passed to us from our great, great grandparents. Today, the chemicals or X-rays we need and use also can affect genes, especially if people are careless about how they handle these things.
Smoking causes changes in the genes of our lungs and other places in the body.
Such a poison can garble a gene's code. The poison can affect the message that a gene sends to cells to tell them what to do, how to assemble, and how to grow. It can undermine the cell's way of correcting mistakes that can occur in the DNA - the chemical chain that carries our genes. Researchers are studying how different people respond differently to harmful substances. They have found that common differences in genes can affect the human body's responses.