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.
Almost every cell in the human body has its own 23 pairs of chromosomes. Exceptions include: ova (egg cells) in female humans and spermatozoa (sperm cells) in male humans each have 23 chromosomes, one randomly selected from each pair.