Holliday's original model assumed that heteroduplex DNA would be present on both chromosomes, but experimental data on yeast refuted this. An updated model by Matt Meselson and Charley Radding in 1975 introduced the idea of branch migration. Further observations in the 1980s led to the proposal of alternate mechanisms for recombination such as the double-strand break model (by Jack Szostak, Frank Stahl, and others) and the single-strand annealing model. A third, the synthesis-dependent strand annealing model, did not involve Holliday junctions.