At a reductional division, the two alleles at a heterozygous locus segregate into different daughter nuclei. Reductional divisions are therefore vulnerable to genetic elements that cause one cell to attack its sister. This danger can be circumvented by creating uncertainty about when reduction occurs. In conventional meiosis, this is achieved by a sequence of two divisions with crossing over. Either the first or the second division can be reductional for most loci. In some red algae, reduction appears to be spread over more than two divisions. The novel reduction sequence of microsporidia creates maximal uncertainty about the time of reduction in two divisions without crossing over.