 In the early 1900s , William Bateson and Reginald Punnett found an exception to one of the principles of inheritance originally described by Gregor Mendel in the 1860s . In contrast to Mendel 's notion that traits are independently assorted when passed from parent to child — for example that a cat 's hair color and its tail length are inherited independent of each other — Bateson and Punnett showed that certain genes associated with physical traits can be inherited together , or genetically linked . In 1911 , after observing that linked traits could on occasion be inherited separately , Thomas Hunt Morgan suggested that " crossovers " can occur between linked genes , where one of the linked genes physically crosses over to a different chromosome . Two decades later , Barbara McClintock and Harriet Creighton demonstrated that chromosomal crossover occurs during meiosis , the process of cell division by which sperm and egg cells are made . Within the same year as McClintock 's discovery , Curt Stern showed that crossing over — later called " recombination " — could also occur in somatic cells like white blood cells and skin cells that divide through mitosis . 
