The genes present on same chromosome do not assort independentaly. These genes are called linked genes and the phenomena as linkage. Therefore, linkage is an exception to law of independent assortment. Bateson and Punnett when working on Lathyrus odoratus (sweet pea) got some results .which do not follow law of independent assortment. According to law of segregation (law of purity of gametes) the genes for each character segregate during gamete formation. As a result of each gamete receive only one factor for each character.