Genes also determine certain physical characteristics, such as eye color,, and are passed on from parents to children. Genes are believed to play a role in some cancers, either by stimulating the growth of cancer cells or by failing to stop them before they grow out of control. These cells are too small for you to see with your eye - you must use a microscope. Every cell contains a nucleus , which is even smaller, but still visible under a microscope. The cell nucleus contains an even smaller set of chromosomes , which can only be detected with special laboratory techniques.
Every chromosome contains DNA, the genetic material that is unique for each living creature.
Along the DNA lie thousands of genes , which are smaller yet. We can detect genes only by advanced analytical techniques such as gene sequencing methods that are currently being used to map the entire human genome. In the future, gene doctors would use a variety of techniques, some similar to current vaccinations, to inject normal genes into a person's body. Other approaches might put genes into mechanical devices to deliver them into the body. Even nanotechnology - the use of very small, even microscopic particles could eventually be part of a gene therapy delivery system.