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E M Dessen

Publications and source records attributed to E M Dessen.

5 recordsLinked to original sources
PubMed2000

Chromosome differentiated populations of Anopheles cruzii: evidence for a third sibling species.

Anopheles cruzii is the most common species of mosquito in Southeast Brazil and a vector of human and monkey malaria. The banding pattern of the ovarian polytene chromosomes and the frequencies of paracentric inversions of individuals from two populations were studied. A new sequence of bands on the sex chromosome, defined as form C, was disclosed. In both populations where forms A (considered as standard) and C are sympatric no heterozygotes were detected. A sequence of events that could account for the observed changes in the banding sequences of the X chromosome forms was proposed. The frequencies of 22 paracentric inversions were used to assess panmixia and the results indicated the presence of two distinct genetic pools in each population. We consider these results as evidence of another sibling species in the taxon cruzii, characterized by a distinctive form of the X chromosome and provisionally designated Anopheles cruzii species C.

Animals↗
PubMed2000

Chromosomal evidence for sibling species of the malaria vector Anopheles cruzii.

An analysis of the ovarian polytene chromosomes of Anopheles cruzii from three localities in Southeast Brazil revealed the existence of two genetic entities within this morphologically uniform taxon. These cryptic species differed in the banding patterns of the X chromosome and 3L arm. A pattern of bands that cannot be explained by the fixation of any of the known inversions in chromosome X was revealed and named chromosomal form B to distinguish it from the standard pattern of this X chromosome, form A. Each chromosomal form is characterized by a different set of inversions. The lack of heterozygotes (A/B) for these X chromosome forms in populations where both forms coexist is evidence of absence or limited gene flow between the two groups.

Animals↗
PubMed1979

A gene that modifies the sex ratio in a bisexual strain of Sciara ocellaris.

The influence of an X-linked recessive mutation, sepia, on the sex determination of a bisexual strain of Sciara ocellaris was studied. It induces an alteration in the sex ratio, especially in the progeny of heterozygous females, increasing the proportion of males. These results cannot be explained by differential fecundity of the female parents of different genotypes nor by differential mortality between the sexes. The occurrence of gynandromorphs indicates that the mutant probably interferes with the processes of X-chromosome elimination. Observations that heterozygous females which received the sepia allele from their mothers produced a higher frequency of gynandromorphs than females which received the mutated allele from their male parents, suggest that the mutation is interfering with the mechanism of chromosome elimination present in the egg cytoplasm.

Animals↗
PubMed1976

Evidence of hormonal control of the nucleolar activity in Sciara ocellaris.

The nucleolus organizing region in the salivary gland of Sciara ocellaris becomes gradually less active as the larvae approach pupation. The cytological visible condensation of the nucleolar puff is paralleled by a decrease in the incorporation of [3H]-uridine into the ribosomal RNA. Alterations in the nucleolar behavior were brought about by extirpation of the neuroendocrine glands at six stages of development. There is a 'critical stage' during the 7th day of the 4th instar when the hormonal stimulus for pupation occurs. If the ligature is performed before this stage the NOR remains expanded and the larval-pupal ecdysis is inhibited; if done later on the NOR condenses at a normal rate and the ligated larvae mount to head-less pupae. These results suggest that inhibition of rRNA synthesis and consequent condensation of the NOR is under the control of the moulting hormone.

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