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.
The DNA in all human cells except eggs and sperm is housed in 46 chromosomes. Eggs and sperm consist of only half that number, 23 chromosomes per cell. Every person inherits one set of chromosomes from their mother (in the egg) and the other set of chromosomes from their father (in the sperm).