Giardia and the other diplomonads are unique in their possession of two nuclei that are similar in appearance, DNA content, transcription, and time of replication. Trophozoites have a ploidy of four and the ploidy of cysts is eight, which in turn raises the question of how Giardia maintains homogeneity between the chromosomes of the same and opposite nuclei. Giardia has been assumed to be primitively asexual and with no means of transferring DNA between nuclei. These assumptions make it very difficult to explain the remarkably low level of allelic heterozygosity (< 0.01%) in the genome isolate, WB. However, all these assumptions are now in doubt with the identification of meiotic genes in Giardi, evidence for recombination among isolates, and the evidence for exchange of genetic material between nuclei during the process of encystation.

from Anaerobic Parasitic Protozoa: Genomics and Molecular Biology

Further reading:

• Anaerobic Parasitic Protozoa
• Acanthamoeba: Biology and Pathogenesis
• Leishmania: After The Genome

Labels: Allelic heterozygosity, Diplomonads, Giardia WB, Ploidy, Trophozoites