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PubMed2002

Stable chromosomal inversion polymorphisms and insecticide resistance in the malaria vector mosquito Anopheles gambiae (Diptera: Culicidae).

Anopheles gambiae Giles has been implicated as a major vector of malaria in Africa. A number of paracentric chromosomal inversions have been observed as polymorphisms in wild and laboratory populations of this species. These polymorphisms have been used to demonstrate the existence of five reproductive units in West African populations that are currently described as incipient species. They have also been correlated with various behavioral characteristics such as adaptation to aridity and feeding preference and have been associated with insecticide resistance. Two paracentric inversions namely 2La and 2Rb are highly ubiquitous in the wild and laboratory populations sampled. Both inversions are easily conserved during laboratory colonization of wild material and one shows significant positive heterosis with respect to Hardy-Weinberg proportions. Inversion 2La has previously been associated with dieldrin resistance and inversion 2Rb shows an association with DDT resistance based on this study. The stability and maintenance of these inversions as polymorphisms provides an explanation for the transmission and continued presence of DDT and dieldrin resistance in a laboratory strain of An. gambiae in the absence of insecticide selection pressure. This effect may also be operational in wild populations. Stable inversion polymorphism also provides a possible mechanism for the continual inheritance of suitable genetic factors that otherwise compromise the fitness of genetically modified malaria vector mosquitoes.

Animals↗
PubMed1997

Mutations induced in Drosophila during space flight.

To examine the possible effects of space radiation on living organisms, fruit flies Drosophila melanogaster were loaded on the US Space Shuttle Endeavour, and after the flight we have analyzed two types of mutations, sex-linked recessive lethal mutations induced in male reproductive cells and somatic mutations which give rise to morphological changes in hairs growing on the surface of wing epidermal cells. Wild type strains and a radiation-sensitive strain mei-41 were used. The frequencies of sex-linked recessive lethal mutations in flight groups were 2 and 3 times higher for wild type Canton-S and mei-41 strains, respectively, than those in ground control groups. By contrast, the frequencies of wing-hair somatic mutations differed little between flight and control groups. The possibility that the space environment causes mutations in certain types of cells such as male reproductive cells, is discussed.

Animals↗
PubMed2004

[Construction of AFLP molecular markers linkage map and localization of green cocoon gene in silkworm (Bombyx mori)].

Based on an improved method of AFLP, AFLP markers were employed for construction of a linkage map and localization of Gc gene used a set of 44 backcross lines( BC1) of silkworm ( Bombyx mori) as a mapping population. In this work, all together 3 956 bands were obtained by 28 pairs of primers and 141.3 bands each primer pair on average. Among them 2 836 bands were in good agreement with the segregation pattern. A total of 1 018 (25.7%) polymorphic AFLP markers were detected. The 693 (68.1%) of polymorphic markers with 1:1 segregation ratio ( P < or = 0.05) were obtained. Furthermore,The analytical model was based on the backcross type and the parameters were set as following: LOD = 3.0, maximum recombination value of 0. 20 and use the command ' group', 'compare', 'try', 'map' and 'ripple' to construct the linkage maps. 407 of the 693 loci were chi2 tested in agreement with 1:1 segregation were divided into 33 linkages by Mapmaker/Exp(Version 3.0), with a total map distance of 3 676.7 cM and a mean distance of 9.1 cM between markers. The morphological gene Gc was located between L-P4T6-107 and L-PT6T4-84 on linkage group 22. In addition, 286 markers were not included in the linkage groups. The efficiency of loci mapping was 58.7%. Among the 33 linkage groups, the morphological marker Gc classically localized on linkage group 15 was relocated on linkage group 22 on the map, suggesting that this molecular linkage group corresponds to linkage group 15 on the linkage map based on morphological characters. All these have laid an important base for the marker assisted breeding of the silkworm.

Animals↗
PubMed2006

Genetic differentiation between the BAMAKO and SAVANNA chromosomal forms of Anopheles gambiae as indicated by amplified fragment length polymorphism analysis.

The main vector of malaria in sub-Saharan Africa, Anopheles gambiae, is subdivided into five chromosomal forms. Three of them (i.e., BAMAKO, SAVANNA, and MOPTI) are found in sympatry in Mali, where MOPTI can be distinguished from the other two forms based on differences in the ribosomal DNA locus. However, no molecular markers are available to distinguish BAMAKO from SAVANNA. We examined the banding patterns of 139 amplified fragment length polymorphism primer combinations in an attempt to identify diagnostic differences between SAVANNA and BAMAKO. Despite screening > 10,000 bands, no diagnostic differences were found. However, additional AFLP analyses indicated that BAMAKO is genetically differentiated from SAVANNA, with a significant Phi(st) value of 0.072. This could indicate that gene flow between these forms is restricted in at least some portion of the genome and the lack of identifiable fixed differences between the two forms is probably due to their recent origin.

Animals↗
PubMed1985

Seasonal variations in indoor resting Anopheles gambiae and Anopheles arabiensis in Kaduna, Nigeria.

A longitudinal study in a guinea savanna area in Northern Nigeria showed that indoor resting samples consisted almost entirely of An. gambiae in the wet season, characterized by relatively lower temperature and higher relative humidity, whereas An. arabiensis predominated in the dry season, characterized by relatively higher temperature and lower relative humidity. A significant change was also observed in the frequency of polymorphic chromosomal inversions in the population of An. gambiae. The inverted arrangements 2Rbc, 2Rd and 2La were found more frequent in the dry season samples as compared to the wet season ones.

Animals↗
PubMed1988

Cytogenetic evidence for two species within the current concept of the malaria vector Anopheles leucosphyrus in Southeast Asia.

Karyotypes and crossing relationships were investigated for three allopatric populations of Anopheles leucosphyrus in Southeast Asia: South Kalimantan, Sumatra and Thailand. The mitotic karyotypes of these populations were similar to those previously observed in other species of the An. leucosphyrus group. Populations from Thailand and South Kalimantan exhibited telocentric and subtelocentric sex chromosomes, respectively, with a distinctive band of intercalary heterochromatin in the X chromosome. Strikingly different submetacentric X and Y chromosomes were observed in the population from Sumatra, and it seems likely that the evolution of these chromosomes occurred through the acquisition of constitutive heterochromatin. Sterile F1 males were observed in crosses between the Sumatra population and the populations from South Kalimantan and Thailand. No genetic incompatibility was observed in crosses between the latter two populations. We believe that the present concept of An. leucosphyrus includes two allopatric species, one inhabiting Borneo, West Malaysia and southern Thailand and one confined to Sumatra.

Animals↗
PubMed1986

Development of a method for the cytological identification of man-biting sibling species within the Simulium damnosum complex.

A method is described for the preparation of adult Malpighian tubule polytene chromosomes from members of the Simulium damnosum complex. This method was used to show that the banding pattern is conserved between adult and larval tissues, and consequently it has been possible to demonstrate that within the S. sanctipauli subcomplex both S. soubrense 'B' and S. sanctipauli bite humans. The degree tubule development is correlated with the gonotrophic cycle and appears to be dependent on food source. This suggests that there is a physiological stage which is optimum for obtaining maximum polyteny for cytotaxonomy.

Animals↗
PubMed1982

Cytogenetic studies on the malaria vector mosquito Anopheles arabiensis Patton in the Awash Valley, Ethiopia.

Blood fed female mosquitoes were collected from human dwellings in the Awash Valley, Ethiopia. Those identified morphologically as A. gambiae s.l. were preserved in Carnoy's fixative for later ovarian polytene chromosomes examination. Only one member of the A. gambiae complex, A. arabiensis, was found by such examination. The polymorphic inversions identified were 2Rb and 3Ra. The frequencies of these inversions were variable in different localities and the former inversion was found to form an altitudinal cline.

Animals↗
PubMed1995

Analysis and in situ mapping of the Adh locus in species of the willistoni group of Drosophila.

The Adh locus was mapped by in situ hybridization with the heterologous biotinylated probe SAC-PAT to the salivary chromosomes of seven species of the willistoni group of Drosophila. Hybridization signals were obtained mainly at a single site to the right arm of chromosome II in six species, but in Drosophila nebulosa two sites hybridized with the same consistency. Southern blot analysis Eco RI-digested genomic DNA of the seven species revealed high molecular weight bands shared by three species, plus the appropriately sized fragment expected, suggesting the presence of Adh pseudogenes in those species.

Alcohol Dehydrogenase↗
PubMed1993

Chromosomal diagnostic criteria for some members of Simulium damnosum complex in east Africa.

Identification of Simulium damnosum s.l. vectors of onchocerciasis demands adequate knowledge of the chromosomal features that distinguish human-biting members from nonanthropophilic forms. In this study, 955 S. damnosum larvae collected from various geographical locations in Tanzania were chromosomally analyzed. 358 larvae from small mountain streams in the northeast and central regions of Tanzania, were identified as mainly Nyamagasani and Sanje forms, with only one Kiwira form. 378 larvae from plain and lowland rivers, also in the northeast and central regions, were identified as Nkusi, Kisiwani and Kibwezi forms. Chromosomal examination of 219 larvae from the southern highlands zone revealed the presence of Kiwira and Nyamagasani forms. A further 27 larvae of S. damnosum complex collected from 5 rivers in Uganda were identified as Sebwe and Nkusi forms. Chromosomal photomicrographs on which the distinguishing characters were based are provided. These observations are discussed in the light of previous studies carried out on the S. damnosum cytological forms in Eastern Africa.

Animals↗
PubMed1993

A pictorial guide to the chromosomal identification of members of the Simulium damnosum Theobald complex in west Africa with particular reference to the Onchocerciasis Control Programme Area.

Simulium damnosum Theobald is made up of a complex of sibling species. Nine species are described in the area covered by the World Health Organisation's Onchocerciasis Control Programme in West Africa (OCP). These are, S. squamosum, S. yahense, S. canctipauli, S. soubrense, S. leonense, S. konkourense, S. damnosum s.s., S. sirbanum and S. dieguerense. All of them are vectors of human onchocerciasis, albeit to different capacities. Reliable species determination presently depends on larval cytotaxonomic criteria. The diagnostic chromosomal inversions and other micromorphological characters used in the identification of the species found in the OCP area are presented with figures for their recognition, some distributional information is also given.

Africa, Western↗
PubMed1996

Resting behaviour, ecology and genetics of malaria vectors in large scale agricultural areas of Western Kenya.

In Kenya indoor and outdoor resting densities of Anopheles arabiensis and Anopheles funestus at the Ahero rice irrigation scheme, and Anopheles gambiae s.s., An. arabiensis and An. funestus at the Miwani sugar belt were assessed for 13 months by pyrethrum spray collections in houses and granaries. The vector's house leaving behaviour was evaluated with exit traps and it was noted that early exophily (i.e., deliberate) was not detected in any of the vectors. Assortative indoor/outdoor resting behaviour was studied by a capture-mark-release-recapture method and showed that in An. arabiensis both indoor and outdoor resting traits were present in the same individuals. Samples of half-gravid female An. gambiae s.l. were chromosomally identified either as Anopheles gambiae s.s. or An. arabiensis and in a subsample chromosomal inversions were read. Anopheles gambiae s.s. and An. arabiensis had the 2Rb inversion but in addition the 2La inversion was found in An. gambiae s.s. and this is an indication of low chromosomal variation. At Ahero An. arabiensis was most abundant when the rice crop was immature and An. funestus when the crop was mature. This succession of vectors facilitated the transmission of malaria throughout the year. At Miwani, An. gambiae s.l. population peaked during the long rains but the proportion of An. arabiensis was highest during the dry season. The indoor resting density of males of the three vector species was less than half of the females.

Agriculture↗
PubMed1997

Location and mapping of an autosomal recessive mutation causing unique phenotypic change in Drosophila bipectinata.

In Drosophila bipectinata, flies with bilateral outgrowths on thorax were detected in sepia eye colour mutant stock. Such thoracic outgrowths have not been reported earlier in any species of Drosophila and appear to be unique phenotypic change in D. bipectinata caused due to autosomal recessive mutation. By using a double recessive mutant stock (se og) and a wild type stock, crosses were made and on the basis of recombination data of F1 females, the og mutation was mapped on the second chromosome of D.bipectinata. Further, D. bipectinata exhibits spontaneous male recombination in low frequency.

Animals↗
PubMed2001

How malleable is the eukaryotic genome? Extreme rate of chromosomal rearrangement in the genus Drosophila.

During the evolution of the genus Drosophila, the molecular organization of the major chromosomal elements has been repeatedly rearranged via the fixation of paracentric inversions. Little detailed information is available, however, on the extent and effect of these changes at the molecular level. In principle, a full description of the rate and pattern of change could reveal the limits, if any, to which the eukaryotic genome can accommodate reorganizations. We have constructed a high-density physical map of the largest chromosomal element in Drosophila repleta (chromosome 2) and compared the order and distances between the markers with those on the homologous chromosomal element (3R) in Drosophila melanogaster. The two species belong to different subgenera (Drosophila and Sophophora, respectively), which diverged 40-62 million years (Myr) ago and represent, thus, the farthest lineages within the Drosophila genus. The comparison reveals extensive reshuffling of gene order from centromere to telomere. Using a maximum likelihood method, we estimate that 114 +/- 14 paracentric inversions have been fixed in this chromosomal element since the divergence of the two species, that is, 0.9-1.4 inversions fixed per Myr. Comparison with available rates of chromosomal evolution, taking into account genome size, indicates that the Drosophila genome shows the highest rate found so far in any eukaryote. Twenty-one small segments (23-599 kb) comprising at least two independent (nonoverlapping) markers appear to be conserved between D. melanogaster and D. repleta. These results are consistent with the random breakage model and do not provide significant evidence of functional constraint of any kind. They support the notion that the Drosophila genome is extraordinarily malleable and has a modular organization. The high rate of chromosomal change also suggests a very limited transferability of the positional information from the Drosophila genome to other insects.

Animals↗