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.
When a sperm cell (with 23 chromosomes from the father), fertilises an egg cell (with 23 chromosomes from the mother), the resulting fertilised egg has 46 chromosomes. Via cell division, it grows into a human, with 46 chromosomes in each of its body cells.