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.
Humans have 46 chromosomes in each cell. During fertilization of the egg, the sperm nucleus containing 23 chromosomes from the paternal side fuses with the nucleus of the egg that contains 23 chromosomes from the maternal side. The result is the zygote that contains 46 chromosomes (23 pairs of chromosomes; one of each pair from either parent).