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.
Human diploid cells contain two sets of 23 chromosomes for a total of 46 chromosomes. When sex cells unite during fertilization, the haploid cells become a diploid cell. The production of sperm cells is known as spermatogenesis. This process occurs continuously and takes place within the male testes. Hundreds of millions of sperm must be released in order for fertilization to take place. The vast majority of sperm released never reach the ovum.