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.
Therefore there is a total of 23 pairs of chromosome in a human body cell. However the human gametes formed by meiosis have haploid number of chromosomes i.e. they have only 23 chromosomes instead of 46; so that after fertilization the zygote has 23 pairs of chromosome(23 from the sperm and 23 from the ovum). There are 23 pairs(46 chromosones)of chromosones in a human body cell.