Inheritance of extranuclear DNA in malaria parasites

• Main Author: Creasey, Alison M.
• Published: University of Edinburgh 1996
• Subjects: 579
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645131

The inheritance pattern of extranuclear DNA in malaria parasites has been investigated in a cross between two different clones of the human malaria parasite Plasmodium falciparum. A 1:1 mixture of gametocytes from the two clones, 3D7 and HB3, had been fed to mosquitoes. In this project, a polymorphism between clones 3D7 and HB3 was identified in the highly conserved mitochrondiral cytochrome b gene of the extranuclear DNA. When this allelic marker was examined in the oocysts from the cross, each hybrid oocyst showed only one form, and never both forms, of the parental alleles. This indicated that extranuclear DNA in P. falciparum is uniparentally inherited. Unexpectedly 58 out of the 59 hybrid oocysts examined showed the 3D7 form and only one oocyst showed the HB3 form of the allele. The sex of the gamete transmitting the extranuclear DNA was investigated using purified preparations of male and of female gametes of the avian malaria parasite P. gallinaceum. Probes for the two extranuclear DNA elements in malaria, the 6kb mitochondrial element and the 35kb plastid-like element, hybridised to the female gamete DNA but not to the male gamete DNA. This led to the conclusion that inheritance of extranuclear DNA is through the female gamete, and implies that the majority of the hybrid oocysts in the 3D7xHB3 cross were of the 3D7female/HB3 male type. Analysis of cross fertilization and self fertilization events in this cross, using nuclear gene alleles, was shown to be in accordance with random mating, falling within the Hardy-Weinberg equilibrium predictions. The existence of the bias in parental contribution to the hybrids revealed by the extranuclear markers in this present work is difficult to reconcile with such random mating.