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.
An egg has 22 chromosomes and one sex chromosome known as the X chromosome. A sperm also has 22 chromosomes and one sex chromosome which can either be an X or a Y chromosome. It is the spermâs chromosome that determines the sex of the baby.