Molecular basis of inheritance involves the study of genes, genetic variations and heredity. It explains how an offspring looks similar to the parents. DNA, RNA and genetic code form the basis of the molecular origin of inheritance. They transmit the hereditary genes from the parents to the offspring. Genetics mainly deals with the study of genes, heredity, and genetic variation. Genes exist on chromosomes and chromosomes are comprised of DNA and proteins. DNA is a molecule that carries genetic information in all living organisms and viruses where it is used in reproduction, functioning, growth, and development. It is a long polymer of deoxyribonucleotides. DNA is a double-helical structure that carries all the genetic information. Its length is determined by the number of nucleotide pairs present in it. It is an acidic substance in the nucleus identified by Friedrich Meischer. Watson and Crick gave its double-helical structure. The chapter covers important topics such as DNA, RNA, the process of replication etc.