Meiotic crossover frequencies show wide variation among organisms. But most organisms maintain at least one crossover per homolog pair (obligate crossover). In Saccharomyces cerevisiae, previous studies have shown crossover frequencies are reduced in the mismatch repair related mutant mlh3D and enhanced in a meiotic checkpoint mutant pch2D by up to twofold at specific chromosomal loci, but both mutants maintain high spore viability. We analyzed meiotic recombination events genome-wide in mlh3D, pch2D, and mlh3D pch2D mutants to test the effect of variation in crossover frequency on obligate crossovers. mlh3D showed $30% genome-wide reduction in crossovers (64 crossovers per meiosis) and loss of the obligate crossover, but nonexchange chromosomes were efficiently segregated. pch2D showed $50% genome-wide increase in crossover frequency (137 crossovers per meiosis), elevated noncrossovers as well as loss of chromosome size dependent double-strand break formation. Meiotic defects associated with pch2Δ did not cause significant increase in nonexchange chromosome frequency. Crossovers were restored to wild-type frequency in the double mutant mlh3D pch2D (100 crossovers per meiosis), but obligate crossovers were compromised. Genetic interference was reduced in mlh3D, pch2D, and mlh3D pch2D. Triple mutant analysis of mlh3D pch2D with other resolvase mutants showed that most of the crossovers in mlh3D pch2D are made through the Mus81-Mms4 pathway. These results are consistent with a requirement for increased crossover frequencies in the absence of genetic interference for obligate crossovers. In conclusion, these data suggest crossover frequencies and the strength of genetic interference in an organism are mutually optimized to ensure obligate crossovers. Meiosis is a reductional division that produces haploid gametes or spores from diploid progenitor cells. Ploidy reduction is achieved by one round of DNA replication, followed by two consecutive nuclear divisions (Meiosis I and II), producing four daughter cells (Roeder 1997). Crossovers promote the formation of chiasma which serves as a physical linkage between two homologs and opposes the spindle generated forces that pull apart the homolog pairs. This opposing set of forces provides the tension necessary to promote proper disjunction of homolog pairs at Meiosis I (Petronczki et al. 2003). Failure to maintain at least one crossover per homolog pair increases the probability of nondisjunction, resulting in aneuploid gametes (Serrentino and Borde 2012). Although crossovers are important for chromosome segregation, nonexchange chromosomes have been observed to segregate accurately forming viable gametes (Hawley et al. 1992;Davis and Smith 2003;Kemp et al. 2004;Newnham et al. 2010;Krishnaprasad et al. 2015). Meiotic crossovers (and noncrossovers) are initiated in S. cerevisiae by 150-170 programmed double-strand breaks (DSBs) formed by an evolutionarily conserved topoisomerase-like protein Spo11 and other