To learn according to which scenario homologous recombination occurred, we checked whether mutation DXho introduced into MatH-RNA3 (just behind 3 0 RAS1) is still present in RNA3 recombinants. In this way, we were able to determine if their 3 0 -UTR was derived from MatH-RNA3 or wtRNA1 molecules. The undertaken analysis revealed that the mutation was present in 20% of recombinants. This result suggested that homologous crossovers preferentially occur between wtRNA1 and MatH-RNA3.