Watson and Crick proposed a model for DNA that, it comprises of two helicaly inter-twined chains tied together by hydrogen bonds and gives the semiconservative model of DNA replication. Meselson and Stahl by using heavy isotope of nitrogen in bacteria confirm the Watson and Cricks semiconservative theory of DNA replication. Avery, MacLeod and McCarty recognized the DNA nature by transforming principle of Pneumococcus bacteria. Bateson and Punnet reported first case of linkage in sweet pea, however they failed to explain the phenomenon correctly.