Linkage of a gene causing malaria refractoriness to Diphenol oxidase-A2 on chromosome 3 of Anopheles gambiae.
An inbred line of the African malaria vector Anopheles gambiae is refractory to development of malaria parasites. It is homozygous for a 4.3-kb Sal I restriction fragment at the Dox-A2 locus, whereas the parent population is polymorphic at this locus, and a susceptible line is homozygous for an alternate 3.85-kb fragment. The Dox-A2 locus is located in the middle of chromosome 3R, in division 33B, and is tightly linked to a cluster of genes including Dopa decarboxylase that are involved in the production of melanin. Because the refractoriness phenotype, melanotic encapsulation of ookinete/oocysts, might involve activation of or alteration in one or more of these genes, we performed genetic crosses to determine whether a previously identified Plasmodium cynomolgi Ceylon refractoriness gene, Pif-C, is linked to Dox-A2. Backcross mosquitoes fed on one infected monkey developed infections of < or = 100 oocysts. About 50% of these mosquitoes appeared phenotypically refractory, as expected for the backcross performed, but gave slight evidence of linkage between a refractoriness gene and Dox-A2. In contrast, females fed on a monkey that yielded higher infection levels, up to > 300 oocysts, showed clear evidence of linkage between a refractoriness gene and Dox-A2. We conclude that this Dox-A2-linked refractoriness gene is expressed under conditions particular to the higher infection levels, or that environmental factors obscured the genetic effect of this gene at lower infection levels.
Romans
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Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Black
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Sakai
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Gwadz
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D000483:Alleles; D000818:Animals; D000852:Anopheles / Q000201:enzymology / Q000235:genetics* / Q000469:parasitology; D004156:Catechol Oxidase / Q000235:genetics*; D003433:Crosses, Genetic; D005260:Female; D008040:Genetic Linkage; D005838:Genotype; D006579:Heterozygote; D006720:Homozygote; D007303:Insect Vectors / Q000201:enzymology / Q000235:genetics* / Q000469:parasitology; D008253:Macaca mulatta; D008288:Malaria / Q000276:immunology / Q000635:transmission; D008297:Male; D005810:Multigene Family; D016789:Plasmodium cynomolgi / Q000502:physiology*; D011897:Random Allocation