Holliday described a mechanism of DNA-strand exchange that attempted to explain gene-conversion events that occur during meiosis in fungi. That model became known as the Holliday Junction. 

"A Holliday junction is a branched nucleic acid structure that contains four double-stranded arms joined. These arms may adopt one of several conformations depending on buffer salt concentrations and the sequence of nucleobases closest to the junction....In biology, Holliday junctions are a key intermediate in many types of genetic recombination, as well as in double-strand break repair. These junctions usually have a symmetrical sequence and are thus mobile, meaning that the four individual arms may slide through the junction in a specific pattern that largely preserves base pairing. Additionally, four-arm junctions similar to Holliday junctions appear in some functional RNA molecules" (Wikipedia article on Holliday Junction, accessed 7-22).