The segregation of homologous chromosomes during the Meiosis I division requires an obligate crossover per homolog pair (crossover assurance). In @entity375 and mammals, @entity68589 and @entity68590 proteins stabilize Holliday junctions and its progenitors to facilitate crossing over. @entity375 @entity68589 /5 hypomorphs were identified recently that reduce crossover levels up to two-fold at specific loci on chromosomes VII, VIII and XV without affecting homolog segregation. We use the @entity68589 - @entity68591 hypomorph to ask if the obligate crossover is insulated from variation in crossover frequencies, using a @entity375 S288c/YJM789 hybrid to map recombination genome wide. The @entity68589 - @entity68591 hypomorph made on average 64 crossovers per meiosis compared to 94 made in wild type and 49 in @entity68589   mutant confirming the defect seen at individual loci on a genome wide scale. Crossover reductions in @entity68589 - @entity68591 and @entity68589   were significant across chromosomes regardless of size, unlike previous observations made at specific loci. The @entity68589 - @entity68591 hypomorph showed reduced crossover interference. Although crossover reduction in @entity68589 - @entity68591 is modest, 42% of the four viable spore tetrads showed non-exchange chromosomes. These results, along with modeling of crossover distribution, suggest the significant reduction in crossovers across chromosomes and the loss of interference compromises the obligate crossover in the @entity68589 hypomorph. The high spore viability of the @entity68589 hypomorph is maintained by efficient segregation of the natural non-exchange chromosomes. Our results suggest variation in crossover frequencies can compromise the obligate crossover and also support a mechanistic role for interference in obligate crossover formation.

Variation in Crossover Frequencies Perturb Crossover Assurance Without Affecting Meiotic Chromosome Segregation in XXXX .

@entity375 :: ('4932', 'Species') :: ['Saccharomyces cerevisiae'] @entity68590 :: ('851401(Tax:4932)', 'Gene') :: ['Msh5'] @entity68591 :: ('p|SUB|R|676|W', 'ProteinMutation') :: ['R676W'] @entity68589 :: ('850545(Tax:4932)', 'Gene') :: ['Msh4', 'msh4']
@entity375 :: (4932,Species) :: ['Saccharomyces cerevisiae']
