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 cells contain 46 chromosomes or 23 homologous pairs (i.e., in huÂ­mans w = 23). The 46 chromosomes of the zygote formed at fertilization are derived equally from the sperm cell and egg cell of the male and female parÂ­ents. Each of these gametes contributes one member of each pair of homologues.