S. Singer and G. Nicolson (1972) introduced the fluid mosaic model. According to it, the biological membranes have two types of protein arranged in a mosaic. Integral or intrinsic protein are movable while extrinsic protein are immovable. This is the most acceptable theory, also called as, quasi fluid model. M. Knoll and E. Ruska (1932) invented the electron microscope using electron beam in a vacuum chamber using electromagnetic lenses. Bateson and Punnet (1906) noticed event of linkage in sweet pea, Lathyrus odoratus. They coined the terms coupling and repulsion for two aspects of linkage.