Parasexuality and mosaic aneuploidy in Leishmania: alternative genetics

•Aneuploidy is generally considered to be deleterious, but is constitutive in Leishmania spp.•Mosaic aneuploidy does not support the formation of gametes in Leishmania.•Mosaic aneuploidy leads to homozygosity, but maintains genetic heterogeneity.•In the context of mosaic aneuploidy, automixis unexpectedly generates heterozygotes.

Reproduction as identical or similar organisms in most biological systems depends on the extreme accuracy of the mitotic (and meiotic) mechanisms involved in the transmission of the genetic material to the two daughter cells. Character recombination and genotype diversification are ensured by the alternation between haploidy and diploidy, which corresponds to the most predominant model in sexually reproducing organisms. In Leishmania, the unique association of high levels of automixis and of constitutive ‘mosaic aneuploidy’ unexpectedly does not lead to loss of heterozygosity but constitutes an alternative for genotype recombination, hence a source of adaptability.