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PubMed1994

Ubiquitin genes and ubiquitin protein location in polytene chromosomes of Drosophila.

Ubiquitin genes are found in Drosophila either as a repeat block or as gene fusions with ribosomal proteins. Here is described the location of a new repeat block in the X chromosome that is present in the strain Canton S but absent in Vallecas. There are also two ubiquitin-ribosomal protein fusion genes located at regions 97A of chromosome 3R and 31E of 2L. Using an anti-ubiquitin antibody in Drosophila polytene chromosomes it is shown that ubiquitin is mainly associated with the compact and stabilized structure that forms the bands rather than with the more decondensed and destabilized protein-DNA structure that forms interbands and puffs.

Animals↗
PubMed2004

Tagging and mapping of a rice gall midge resistance gene, Gm8, and development of SCARs for use in marker-aided selection and gene pyramiding.

Using amplified fragment length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs), we have tagged and mapped Gm8, a gene conferring resistance to the rice gall midge (Orseolia oryzae), a major insect pest of rice, onto rice chromosome 8. Using AFLPs, two fragments, AR257 and AS168, were identified that were linked to the resistant and susceptible phenotypes, respectively. Another resistant phenotype-specific marker, AP19(587), was also identified using RAPDs. SCAR primers based on the sequence of the fragments AR257 and AS168 failed to reveal polymorphism between the resistant and the susceptible parents. However, PCR using primers based on the regions flanking AR257 revealed polymorphism that was phenotype-specific. In contrast, PCR carried out using primers flanking the susceptible phenotype-associated fragment AS168 produced a monomorphic fragment. Restriction digestion of these monomorphic fragments revealed polymorphism between the susceptible and resistant parents. Nucleotide BLAST searches revealed that the three fragments show strong homology to rice PAC and BAC clones that formed a contig representing the short arm of chromosome 8. PCR amplification using the above-mentioned primers on a larger population, derived from a cross between two indica rice varieties, Jhitpiti (resistant parent) and TN1 (susceptible parent), showed that there is a tight linkage between the markers and the Gm8 locus. These markers, therefore, have potential for use in marker-aided selection and pyramiding of Gm8 along with other previously tagged gall midge resistance genes [ Gm2, Gm4(t), and Gm7].

Animals↗
PubMed2004

Germline cyst development and imprinting in male mealybug Planococcus citri.

In the epigenetic modifications involved in the phenomenon of imprinting, which is thought to take place during gametogenesis, one of the primary roles is exerted by histone tail modifications acting on chromatin structure. What is more, in insects like mealybugs, with a lecanoid chromosome system, imprinting is strictly related to sex determination. In many diverse species gametes originate in specific, highly evolutionarily conserved structures called germline cysts. The use of staining techniques specific for fusomal components like F-actin has allowed us to describe for the first time the morphogenesis of male germline cysts in the mealybug Planococcus citri. Antibodies to anti-methylated lysine 9 of histone H3 (MeLy9-H3) and anti-heterochromatin protein 1 (HP1) were used during cyst formation to investigate the involvement of these epigenetic modifications in the phenomenon of imprinting and their possible concerted action in sex determination in P. citri. These observations indicate: (i) a specific role for F-actin in the segregation, typical of the lecanoid chromosome system, of genomes of paternal origin; (ii) that the two vital gametes originating from a given meiosis, although carrying the same genome, differ in the levels of both MeLy9-H3 and HP1, one of them being more heavily labelled by both antibodies.

Actins↗
PubMed2006

Inversion polymorphism and a new polytene chromosome map of Zaprionus indianus Gupta (1970) (Diptera: Drosophilidae).

Zaprionus indianus is a recent invader in Brazil and was probably introduced from the West Afrotropical zone. So far, studies regarding its chromosomal polymorphism were limited to India. We found that Brazilian populations were very different from Indian ones. Five new inversions have been discovered. In(II)A, already described in India, where it is quite common, has also been found in Brazil, where it is very rare. The X-chromosome has three inversions; In(X)Na, In(X)Ke and In(X)Eg, which are frequent in all Brazilian populations studied. In every case, we observed strong linkage disequilibrium among these gene arrangements. During the primary collection period (2001-2002), we noticed a significant positive correlation between the frequency of these inversions and latitude, but this was not confirmed in later investigations. Rearrangement In(IV)EF was also common in all populations, while inversion In(V)B was only found in southern populations. Our data suggest that the founders that recently invaded Brazil were polymorphic for the six inversions observed. The place of origin might be identified more precisely by investigating West African populations. In order to facilitate further investigations, we present an updated polytene chromosome photomap, locating the breakpoints of every inversion observed in Brazilian populations.

Animals↗
PubMed1976

A new sex-linked mutant short wing in Aedes aegypti.

A spontaneous recessive sex-linked mutant short wing has been discovered in the mosquito Aedes aegypti. It is situated less than one cross-over unit from the sex determining locus. In homozygous females, flight is impaired and the survival and fecundity is markedly subnormal. Two possible uses of this gene for genetic control operations are envisaged: (a) to provide automatic sexing of males for release and (b) enhancement of the population control potential of other available genetics systems.

Aedes↗
PubMed2002

Evidence for genetic differentiation between the molecular forms M and S within the Forest chromosomal form of Anopheles gambiae in an area of sympatry.

We studied genetic variation at ten microsatellite DNA loci in Anopheles gambiae populations from the Forest chromosomal form collected in four villages in Cameroon (Central Africa). Both recently described M and S molecular forms occur in sympatry in this area. Geographic differentiation within form was low (Fst < 0.017) despite geographical distance between collection sites ranging from 35 to 350 km. However, higher (Fst > 0.035) and statistically significant levels of genetic differentiation were observed between forms, being the highest between sympatric M and S populations collected within the same village. Results were consistent across all loci spread throughout the genome, therefore reflecting a genome-wide pattern. Considering previous findings of strong assortative mating within forms and general lack of hybrids in areas of sympatry, we propose that there is now sufficient direct and indirect evidence to consider both M and S molecular forms of An. gambiae as distinct species that have probably speciated recently.

Animals↗
PubMed1998

Molecular analysis and chromosome mapping of the H2A, H3 and H4 histone genes from the malaria vector Anopheles gambiae.

In this article we report the cloning and analysis of PCR generated fragments that encode H2A, H3 and H4 histone genes from the malaria vector An. gambiae. Sequence analysis indicated that some conservative changes are present in the An. gambiae H2A and H4 genes as compared with histone genes from other organisms. Divisional mapping showed that these genes map in division 20 on the left arm of the second chromosome. Southern blot experiments and the molecular characterization of the genomic fragment containing the H2A, H2B, H3 and H4 genes showed that they are organized in a cluster with an orientation different from the one found in other dipterans.

Amino Acid Sequence↗
PubMed1997

Chromosomal homology and molecular organization of Muller's elements D and E in the Drosophila repleta species group.

Thirty-three DNA clones containing protein-coding genes have been used for in situ hybridization to the polytene chromosomes of two Drosophila repleta group species, D. repleta and D. buzzatii. Twenty-six clones gave positive results allowing the precise localization of 26 genes and the tentative identification of another nine. The results were fully consistent with the currently accepted chromosomal homologies and in no case was evidence for reciprocal translocations or pericentric inversions found. Most of the genes mapped to chromosomes 2 and 4 that are homologous, respectively, to chromosome arms 3R and 3L of D. melanogaster (Muller's elements E and D). The comparison of the molecular organization of-these two elements between D. melanogaster and D. repleta (two species that belong to different subgenera and diverged some 62 million years ago) showed an extensive reorganization via paracentric inversions. Using a maximum likelihood procedure, we estimated that 130 paracentric inversions have become fixed in element E after the divergence of the two lineages. Therefore, the evolution rate for element E is approximately one inversion per million years. This value is comparable to previous estimates of the rate of evolution of chromosome X and yields an estimate of 4.5 inversions per million years for the whole Drosophila genome.

Animals↗
PubMed1998

Quantitative trait loci for honey bee stinging behavior and body size.

A study was conducted to identify quantitative trait loci (QTLs) that affect colony-level stinging behavior and individual body size of honey bees. An F1 queen was produced from a cross between a queen of European origin and a drone descended from an African subspecies. Haploid drones from the hybrid queen were individually backcrossed to sister European queens to produce 172 colonies with backcross workers that were evaluated for tendency to sting. Random amplified polymorphic DNA markers were scored from the haploid drone fathers of these colonies. Wings of workers and drones were used as a measure of body size because Africanized bees in the Americas are smaller than European bees. Standard interval mapping and multiple QTL models were used to analyze data. One possible QTL was identified with a significant effect on tendency to sting (LOD 3.57). Four other suggestive QTLs were also observed (about LOD 1.5). Possible QTLs also were identified that affect body size and were unlinked to defensive-behavior QTLs. Two of these were significant (LOD 3.54 and 5.15).

Animals↗
PubMed1998

Genetic mapping of a major locus controlling pyrethroid resistance in Tribolium castaneum (Coleoptera: Tenebrionidae).

Tribolium castaneum (Herbst) strain QTC279 is highly resistant to deltamethrin and other synthetic pyrethroids. This strain was shown to carry at least 1 resistance gene, PyR-1, on linkage group 9, approximately 20 map units from the visible mutant marker, pearl. Three-point mapping involving pearl and another visible mutant marker, cola, indicated a gene order of pearl-cola-PyR-1. Evidence of a 2nd LG9-linked resistance factor (R) mapping in the gene order R-p-co was also observed. Other resistance factors were clearly present in QTC279, but were not genetically mapped. Piperonyl butoxide, an inhibitor of cytochrome P450-mediated oxidative metabolism, significantly increased the toxicity of deltamethrin to a strain derived from QTC279 that carries PyR-1, strain pR. Compared to susceptible beetles, QTC279 and pR had elevated and comparable levels of cytochrome P450 protein. The significance of pyrethroid resistance in T. castaneum is discussed.

Animals↗
PubMed2001

Integration of a B chromosome into the A genome of a wasp.

B chromosomes are genome symbionts, the presence of which in many eukaryote species is explained, in most cases, by their violation of Mendelian rules, usually based on meiotic or mitotic instability, leading to their accumulation in the germ line (drive). However, B chromosome integration into the genome as a regular member of the chromosome set should imply the loss of drive. A possible way of bypassing this difficulty is to regularize meiosis when the B chromosome is frequent in the population, in order to yield gametes with one B chromosome. In diploid organisms, this task needs to be achieved in the two sexes, but in haplodiploids the problem simplifies to only the diploid sex. We have found, to the authors' knowledge, the first evidence of a B chromosome that is regularizing its meiotic behaviour and limiting its number to one B chromosome per haploid genome, the same dosage as the standard (A) chromosomes, in the solitary wasp Trypoxylon albitarse. It suggests a possible mechanism for B chromosome integration as a regular member of the chromosome complement.

Animals↗
PubMed1995

The coalescent process and background selection.

Some statistical properties of gene trees are described for a model with background deleterious mutations. It is argued that the history of a small sample of genes under this model is a continuous time Markov chain that quickly reaches stationarity. This observation leads to simple expressions for the expected nucleotide diversity and suggests that the frequency spectrum in small samples should be approximately the same as under a strict neutral model. The results concerning expected nucleotide diversity are compared with observed variation on the third chromosome of Drosophila melanogaster.

Animals↗
PubMed2006

Exceptionally high levels of recombination across the honey bee genome.

The first draft of the honey bee genome sequence and improved genetic maps are utilized to analyze a genome displaying 10 times higher levels of recombination (19 cM/Mb) than previously analyzed genomes of higher eukaryotes. The exceptionally high recombination rate is distributed genome-wide, but varies by two orders of magnitude. Analysis of chromosome, sequence, and gene parameters with respect to recombination showed that local recombination rate is associated with distance to the telomere, GC content, and the number of simple repeats as described for low-recombining genomes. Recombination rate does not decrease with chromosome size. On average 5.7 recombination events per chromosome pair per meiosis are found in the honey bee genome. This contrasts with a wide range of taxa that have a uniform recombination frequency of about 1.6 per chromosome pair. The excess of recombination activity does not support a mechanistic role of recombination in stabilizing pairs of homologous chromosome during chromosome pairing. Recombination rate is associated with gene size, suggesting that introns are larger in regions of low recombination and may improve the efficacy of selection in these regions. Very few transposons and no retrotransposons are present in the high-recombining genome. We propose evolutionary explanations for the exceptionally high genome-wide recombination rate.

Animals↗
PubMed1995

Toward a physical map of Aedes aegypti.

Labelled recombinant cosmids were used as in situ hybridization probes to Aedes aegypti metaphase chromosomes. The cosmid probes yielded paired signals, one on each arm of sister chromatids, and they were ordered along the three chromosomes. In total, thirty-seven different probes were mapped to the three chromosomes of Ae. aegypti (2n = 6): twenty-eight to chromosome 1, six to chromosome 2, and six to chromosome 3. These results represent an initial stage in the generation of a physical map of the Ae. aegypti genome.

Aedes↗
PubMed1996

Four new cytotypes of the onchocerciasis vector blackfly Simulium guianense in Brazil.

Simulium (Trichodagmia) guianense is an important Amazonian vector of onchocerciasis. Examination of the polytene chromosome banding patterns of larvae from five sites in Brazil revealed the occurrence of four cytotypes, designated A, B, C and D. The chromosomal standard, Simulium guianense A, occurred at two localities in Goias State (on the Rio Tocantins and Rio Mucambão) where it was the only cytotype. The other three sites examined yielded one different cytotype from each: B from Rio Oyapoque in Amapa State, C from Rio Tocantins in Maranhão State, and D from Rio Xingu in Para State. All cytotypes differed by at least two fixed inversions, but a sex determining system was not evident in any cytotype. As the cytotypes have been found allopatrically it is not certain that they represent sibling species; sampling of sympatric populations would resolve this. During certain times of the year, voracious anthropophagy by S.guianense sensu lato occurs at the localities sampled for cytotypes A, C and D (biting data are not available for the cytotype B locality). In some other areas, however, S.guianense s.l. is entirely zoophilic. Further studies are needed, therefore, to elucidate the biting habits, vectorial capacity, geographic distribution and taxonomic status of these four, and perhaps additional, cytotypes comprising the S.guianense complex.

Animals↗