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.
Sperm contains 23 chromosomes. An egg contains 23 chromosomes. The zygote (a fertilized egg) contains 46 chromosomes. Yet, it is also important to consider that the egg completes meiosis before joining with the sperm, thereby shedding half of its 46 chromosomes into a polar body that adjoins the zona pelucida lining.