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Chromosomal inversions are prevalent in mosquito species but polytene chromosomes are difficult to prepare and visualize in members of the tribe Aedinii and thus there exists only indirect evidence of inversions. We constructed an F(1) intercross family using a P(1) female from a laboratory strain of Aedes aegypti aegypti (Aaa) and a P(1) male Aedes aegypti formosus (Aaf) from a strain collected from south-eastern Senegal. Recombination rates in the F(2) offspring were severely reduced and genotype ratios suggested a deleterious recessive allele on chromosome 3. The F(2) linkage map was incongruent in most respects with the established map for Aaa. Furthermore, no increased recombination was detected in F(5) offspring. Recombination rates and gene order were consistent with the presence in Aaf of at least four large inversions on chromosome 1, a single small inversion on chromosome 2 and three inversions on chromosome 3.

Background: The malaria vector Anopheles gambiae is polymorphic for chromosomal inversions on the right arm of chromosome 2 that segregate nonrandomly between assortatively mating populations in West Africa. One such inversion, 2Rj, is associated with the BAMAKO chromosomal form endemic to southern Mali and northern Guinea Conakry near the Niger River. Although it exploits a unique ecology and both molecular and chromosomal data suggest reduced gene flow between BAMAKO and other A. gambiae populations, no molecular markers exist to identify this form., Methods: To facilitate study of the BAMAKO form, a PCR assay for molecular karyotyping of 2Rj was developed based on sequences at the breakpoint junctions. The assay was extensively validated using more than 700 field specimens whose karyotypes were determined in parallel by cytogenetic and molecular methods. As inversion 2Rj also occurs in SAVANNA populations outside the geographic range of BAMAKO, samples were tested from Senegal, Cameroon and western Guinea Conakry as well as from Mali., Results: In southern Mali, where 2Rj polymorphism in SAVANNA populations was very low and most of the 2Rj homozygotes were found in BAMAKO karyotypes, the molecular and cytogenetic methods were almost perfectly congruent. Elsewhere agreement between the methods was much poorer, as the molecular assay frequently misclassified 2Rj heterozygotes as 2R+j standard homozygotes., Conclusion: Molecular karyotyping of 2Rj is robust and accurate on 2R+j standard and 2Rj inverted homozygotes. Therefore, the proposed approach overcomes the lack of a rapid tool for identifying the BAMAKO form across developmental stages and sexes, and opens new perspectives for the study of BAMAKO ecology and behaviour. On the other hand, the method should not be applied for molecular karyotyping of j-carriers within the SAVANNA chromosomal form.