Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens. Particular substances have been linked to specific types of cancer. Tobacco smoking is associated with many forms of cancer, and causes 90% of lung cancer.
Human diploid cells have 46 chromosomes and human haploid gametes (egg and sperm) have 23 chromosomes. Retroviruses that contain two copies of their RNA genome in each viral particle are also said to be diploid.
In humans (except in red blood cells) there are 46 chromosomes in all body cells - 23 pairs. Each pair of chromosomes is numbered and has its own particular genes. In gametogenesis, (the production of sperm and eggs) this number is reduced to 23. Only one chromosome of a pair can be inherited.