 In 1930 , McClintock was the first person to describe the cross @-@ shaped interaction of homologous chromosomes during meiosis . The following year , McClintock and Creighton proved the link between chromosomal crossover during meiosis and the recombination of genetic traits . They observed how the recombination of chromosomes seen under a microscope correlated with new traits . Until this point , it had only been hypothesized that genetic recombination could occur during meiosis , although it had been shown genetically . McClintock published the first genetic map for maize in 1931 , showing the order of three genes on maize chromosome 9 . This information provided necessary data for the crossing @-@ over study she published with Creighton ; they also showed that crossing @-@ over occurs in sister chromatids as well as homologous chromosomes . In 1938 , she produced a cytogenetic analysis of the centromere , describing the organization and function of the centromere , as well as the fact that it can divide . 
