However, for heterochiasmate species, three problems with the Haldane-Huxley pleiotropy explanation were discovered [7,8]. The first problem arose when substantial variation in male-female differences in recombination rate was found between pairs of autosomes within mice [8] and Tribolium [9,10], and between genotypes for the same pair of autosomes [11]. The second problem was the discovery that hermaphrodite species (the platyhelminth Dendrocoelum [12] and the plant Allium [13]) may present strong heterochiasmy between male and female meiosis despite having no sex chromosomes or even sex-determining loci. The third problem was the discovery of species in which the heterogametic sex recombines more than the homogametic one (e.g., in some Triturus species) [14]. Because of these contradictory observations, variation in heterochiasmy has remained difficult to explain because of the absence of an alternative theory as well as the lack of a clear pattern in the data.