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.
In meiosis, however, the resultant cell has only half the necessary DNA: 23 chromosomes, one from each pair. During conception, the 23 chromosomes from the sperm and the 23 chromosomes from the egg are combined to create a human fetus with 46 chromosomes.These are also called body cells. Sperm Sperm are produced in vast quantities in the testicles, and sperm production is a constant cycle in the body.