Genetic linkage between malathion and dieldrin resistance in Anopheles arabiensis

A strain of Anopheles arabiensis resistant to both malathion and dieldrin was crossed and backcrossed to a susceptible strain. The progeny were tested on each insecticide in turn. Less than 50% mortality in the second insecticide exposure among the backcross progeny indicated linkage between the resistance genes. In a backcross of A. gambiae X A. arabiensis hybrids a recombination rate of 7.5% was observed. A Y-translocation strain of A. arabiensis showed less than 2.8% recombination between the resistance genes. It is impossible to confirm the genotype of apparent recombinants using existing stocks, but the two resistance mechanisms are biochemically distinguishable. If the two genes are very closely linked, linkage disequilibrium could influence the consequences of switching to malathion spraying after dieldrin resistance has evolved.     

Genes controlling malathion resistance in a laboratory-selected population of Drosophila melanogaster

The chromosomal locations of several genes responsible for increased malathion resistance in a laboratory-selected population of Drosophila melanogaster have been determined. These genes appear to be involved in the regulation of microsomal cytochrome P-450. A major gene on chromosome 2 (2-64) and at least two genes on chromosome 3 (near 3-58) control increased mixed function oxidase activity, and both larval and adult malathion resistance. Although the chromosome 2 locus was not associated with a significant increase in cytochrome P-450 content, SDS polyacrylamide gel electrophoresis of microsomal proteins detected increased silver staining of a polypeptide having a relative molecular mass (Mr) of about 52,000. Microsomes from strains carrying the chromosome 3 factors for resistance contained more cytochrome P-450 and increased amounts of two heme-staining protein bands (Mr = 50,000 and 54,000). The genes regulating these proteins were closely linked to striped at 3-62 and probably identical to the loci responsible for malathion resistance and increased mixed function oxidase activity. Other R genes on both chromosomes 2 and 3 as well as target resistance were required for the full expression of malathion resistance in the selected Drosophila population. Exposure of this Drosophila melanogaster population to malathion selected a polygenic system for the oxidative metabolism of insecticide.     

Polymorphism of M factors in populations of the housefly, Musca domestica L., in Turkey

M factors, which determine maleness in Musca domestica, were found on the second, third, fourth and fifth linkage groups in housefly populations of Turkey. As in European populations, the male-determining factor was more frequently located on linkage group III (MIII). Some males homozygous or double heterozygous for M factors were identified. Deviations from a 1:1 sex ratio in favour of males, as well as mosaics for somatic marker mutations and sexual mosaics (gynandromorphs), were also observed. The results reveal an extensive polymorphism in the sex-determining system.     

Location of genes on chromosome arms in the Anopheles gambiae group of species and their correlation to linkage data for other anopheline mosquitoes

The use of paracentric inversions as genetic markers in the Anopheles gambiae group of mosquitoes is described. The gene for dieldrin resistance is assigned to chromosome 2 which in turn is correlated to the previous assignment of the gene to linkage group II. The locus of the enzyme phosphoglucomutase 2 (Pgm 2) is similarly assigned to chromosome 2 and evidence is presented for possible linkage between Pgm 2 and dieldrin resistance. There was no linkage or correlation of chromosome 2 and loci of the enzymes superoxide dismutase (Sod) and octanol dehydrogenase (Odh). These genes are therefore assumed to be on chromosome 3 (linkage group III). Evidence that such gene linkage group/chromosome correlations may extend to other species for which chromosome maps and homologies have been worked out is discussed.     

Interactions of Differentiated Primary Sex Factors in CHIRONOMUS TENTANS

Different populations of Chironomus tentans, possibly representing geographically isolated races, have two differentiated genic mechanisms of sex determination involving either a dominant male-determining factor in the left arm of chromosome 1 or a dominant female-determining factor at the right tip of chromosome 1. In crosses between these populations, the male-determining factor is epistatic to the female-determining factor. No evidence of intersexuality has been found in such crosses.     

Induction and cleavage of Salmonella typhimurium UmuD protein

Summary Two different chromosomal locations of major genes controlling extreme resistance to potato virus X (PVX) were found by restriction fragment length polymorphism (RFLP) analysis of two populations segregating for the resistance. The resistance geneRx1 mapped to the distal end of chromosome XII, whereasRx2 was located at an intermediate position on linkage group V in a region where reduced recombination and segregation distortion have also been observed. These linkage anomalies were due to abnormal behaviour of the chromosome contributed by the resistant parent P34. The results presented were obtained using two different strategies for mapping genes of unknown location. One approach was the use of probes revealing polymorphic loci spread throughout the genome and resulted in the mapping ofRx1. The second approach was based on the assumption of possible linkage between the resistance gene and clone-specific DNA fragments introduced from a wild potato species.Rx2 was mapped by adopting this strategy.     

A detailed linkage map of medaka, Oryzias latipes: comparative genomics and genome evolution

We mapped 633 markers (488 AFLPs, 28 RAPDs, 34 IRSs, 75 ESTs, 4 STSs, and 4 phenotypic markers) for the Medaka Oryzias latipes, a teleost fish of the order Beloniformes. Linkage was determined using a reference typing DNA panel from 39 cell lines derived from backcross progeny. This panel provided unlimited DNA for the accumulation of mapping data. The total map length of Medaka was 1354.5 cM and 24 linkage groups were detected, corresponding to the haploid chromosome number of the organism. Thirteen to 49 markers for each linkage group were obtained. Conserved synteny between Medaka and zebrafish was observed for 2 independent linkage groups. Unlike zebrafish, however, the Medaka linkage map showed obvious restriction of recombination on the linkage group containing the male-determining region (Y) locus compared to the autosomal chromosomes.     

Organophosphorus insecticide resistance inDrosophila melanogaster populations

Natural variation inDrosophila melanogaster populations for mixed function oxidase activity and organophosphorus resistance was studied by sampling iso-chromosomal lines and laboratory selection. A 20-fold variation in malathion LC₅₀ was found among a sample of 25 third chromosomes from a Raleigh, North Carolina, population. These chromosomes were combined in a population that was selected for malaoxon (a toxic metabolite of malathion) resistance over 12 generations. Response to selection was rapid—within three generations—but small, less than two-fold increase in malathion LC₅₀. Mixed function oxidase activity, as assayed by 7-ethoxycoumarin-O-deethylase, increased in parallel with malathion resistance in the selected population. In spite of the fact that this population was initially formed from strains which were homozygous for chromosome III, after 12 generations of selection for malaoxon resistance only a minority of third chromosomes could be isolated as homozygous combinations. This suggests that selection favoured heterozygous combinations of alleles with decreased fitness in the homozygous state. In a second study, a sample of 39 iso-female lines were collected from a Vineland, Ontario, population. Imidan? (phosmet) LC₅₀ varied 20-fold among these iso-female lines and was strongly correlated with increased 7-ethoxycoumarin-O-deethylase activity. The distribution of 7-ethoxycoumarin-O-deethylase activity was bimodal and estimates of the effective number of segregating factors by Wright’s formula were consistent with a single gene controlling extreme 7-ethoxycoumarin-O-deethylase activity differences. Vineland flies responded rapidly to selection for imidan resistance, but as with malaoxon selection only to a small degree. The 7-ethoxycoumarin-O-deethylase activity increased in imidan-selected flies to the level of the most resistant iso-female line from the sampled population. The major part of selected imidan resistance and all of the increased 7-ethoxycoumarin-O-deethylase activity were attributed to third chromosomal genes. The results suggest that theseDrosophila populations contained a polymorphism for a major factor on chromosome III controlling elevated mixed function oxidase activity together with associated organophosphorus resistance. This polymorphism provided the immediate response to insecticide selection. Other genes have minor effects and combine to give a multifactorial response to selection over longer periods of time.     

Principal component for metabolic syndrome risk maps to chromosome 4p in Mexican Americans: the San Antonio Family Heart Study

Metabolic syndrome refers to the clustering of disease conditions such as insulin resistance, hyperinsulinemia, dyslipidemia, hypertension, and obesity. To explore the genetic predispositions of this complex syndrome, we conducted a principal components analysis using data on 14 phenotypes related to the risk of developing metabolic syndrome. The subjects were 566 nondiabetic Mexican Americans, distributed in 41 extended families from the San Antonio Family Heart Study. The factor scores obtained from these 14 phenotypes were used in multipoint linkage analysis using SOLAR. Factors were identified that accounted for 73% of the total variance of the original variables: body size-adiposity, insulin-glucose, blood pressure, and lipid levels. Each factor exhibited evidence for either significant or suggestive linkage involving four factor-specific chromosomal regions relating to chromosomes 1, 3, 4, and 6. Significant evidence for linkage of the lipid factor was found on chromosome 4 near marker D4S403 (LOD = 3.52), where the cholecystokinin A receptor (CCKAR) and ADP-ribosyl cyclase 1 (CD38) genes are located. Suggestive evidence for linkage of the body size-adiposity factor to chromosome 1 near marker D1S1597 (LOD = 2.53) in the region containing the nuclear receptor subfamily 0, group B, member 2 gene (NROB2) also was observed. The insulin-glucose and blood pressure factors were linked suggestively to regions on chromosome 3 near marker D3S1595 (LOD = 2.20) and on chromosome 6 near marker D6S 1031 (LOD = 2.08), respectively. In summary, our findings suggest that the factor structures for the risk of metabolic syndrome are influenced by multiple distinct genes across the genome.     

对家蚕第18连锁群隐性基因elp、ch-2和mln测交系的分子定位分析

家蚕长形卵(elp)、第二隐性赤蚁(ch-2)、暗化型(mln)均为第18染色体上的隐性突变, 在经典连锁图谱上的顺序和遗传距离已经排定。文章采用正常卵、正常黑蚁及正常白蛾品种P50与包含此3个隐性突变的三隐性测交系W18组配正反交群体, F1回交W18后获得回交群体(P50×W18)♀×W18♂ 和W18♀×(P50×W18)♂, 分别记作BC1F和BC1M, 利用已构建的家蚕SSR分子连锁图谱和根据家蚕基因组精细图设计的STS标记, 对这3个突变基因elp、ch-2、mln进行了分子定位研究, 并根据家蚕基因组精细图, 将第18连锁群的经典遗传图、分子连锁图和基因组物理图进行了对应。整合后的图谱遗传距离为94.2 cM, 突变基因和分子标记的排列顺序分别与形态标记连锁图和基因组精细图相一致, 研究结果对家蚕第18 染色体上其他突变的定位与克隆有重要的借鉴作用。     

Contributions of three-site mutations in acetylcholinesterase and cytochrome P450 to genetic variation in susceptibility to organophosphate insecticides within a natural population of Drosophila melanogaster

In this study, we attempted to elucidate the two resistance factors conferring resistance to organophosphates within the Katsunuma population of Drosophila melanogaster (Meigen), one of which has been mapped on the second chromosome and the other on the third chromosome. With regard to the second chromosome factor, we tested susceptibility to malathion of 54 recombinant inbred lines with recombination between ltd and vg. Analyses of variance (ANOVAs) showed highly significant variation in susceptibility to malathion between recombinant lines. In addition, susceptibility of the second-chromosome resistant line to malathion was increased with additional application of piperonyl butoxide, suggesting a member of the Cyp gene family located between ltd and vg. With regard to the third-chromosome factor, we conducted inhibition assays of acetylcholinesterase (AChE) with respect to fenitroxon and carbaryl, to evaluate the contribution of mutated AChE to organophosphate resistance within the Katsunuma population. I ₅₀ values of resistant lines, isolated from this population, were about 15 times higher for fenitroxon, and about two times higher for carbaryl, than those of susceptible lines, suggesting the contribution of mutated AChE to organophosphate resistance within the Katsunuma population. We further investigated the genetic variation in the acetylcholinesterase (Ace) gene within the newly collected Katsunuma population, by using the allele-specific polymerase chain reaction (PCR) approach, and revealed that within this population there were high frequencies of resistant-type mutations at three sites in the Ace gene, which play critical roles in altering sensitivity of AChE to organophosphate and carbamate insecticides.     

Identification of the Sex-Determining Region of the Ceratitis Capitata Y Chromosome by Deletion Mapping

In the medfly Ceratitis capitata, the Y chromosome is responsible for determining the male sex. We have mapped the region containing the relevant factor through the analysis of Y-autosome translocations using fluorescence in situ hybridization with two different probes. One probe, the clone pY114, contains repetitive, Y-specific DNA sequences from C. capitata, while the second clone, pDh2-H8, consists of ribosomal DNA sequences from Drosophila hydei. Clone pY114 labeled most of the long arm and pDh2-H8 hybridizes to the short arm and the centromeric region of the long arm. In 12 of the analyzed 19 Y-autosome translocation strains, adjacent-1 segregation products survive to the late pupal or even adult stage and can, therefore, be sexed. This was correlated with the length of the Y fragment still present in these aberrant individuals and allowed us to map the male-determining factor to a region of the long arm representing ~15% of the entire Y chromosome. No additional factors, affecting for example fertility, were detected outside the male-determining region.     

Identification and mapping of the replication genes of an R factor, R100-1, integrated into the chromosome of Escherichia coli K-12

A stable Hfr strain of Escherichia coli K-12 was obtained by integrative suppression by an R factor, R100-1. The R factor was integrated into the right of 81 min, and chromosome transfer occurred counterclockwise. Mating experiments revealed two linkage groups of genes on the R factor. Drug-resistant transductants of a dnaA-ts recipient from an R-factor Hfr and from an R(+) strain differ in their drug resistance patterns, temperature sensitivity, and transferability of drug resistance as well as chromosome markers. Transductants that transferred chromosome markers were further classified as to the origin and direction of chromosome transfer. For temperature-sensitive transductants, the reversion frequency to temperature resistance was determined, and these revertants were scored for transfer of drug resistance as well as chromosome markers. Two genes responsible for integrative suppression (designated as repA) and the other for autonomous replication (designated as repB) were identified and mapped. The arrangement of genes on the R factor is... (sul, str, cml)... repA... tra... (tet, repB).... The map of the autonomously replicating R factor is probably a circle connecting both sides of this linear map. Thus, a method has been established to map a plasmid that could not finely be analyzed under autonomous state by transduction. It also permits genetic analysis of genes responsible for replication of the plasmid without making use of a conditional mutant of itself but with that of the host, dnaA.     

Polymorphism and differentiation of rainbow trout Y chromosomes.

Most fish species show little morphological differentiation in the sex chromosomes. We have coupled molecular and cytogenetic analyses to characterize the male-determining region of the rainbow trout (Oncorhynchus mykiss) Y chromosome. Four genetically diverse male clonal lines of this species were used for genetic and physical mapping of regions in the vicinity of the sex locus. Five markers were genetically mapped to the Y chromosome in these male lines, indicating that the sex locus was located on the same linkage group in each of the lines. We also confirmed the presence of a Y chromosome morphological polymorphism among these lines, with the Y chromosomes from two of the lines having the more common heteromorphic Y chromosome and two of the lines having Y chromosomes morphologically similar to the X chromosome. The fluorescence in situ hybridization (FISH) pattern of two probes linked to sex suggested that the sex locus is physically located on the long arm of the Y chromosome. Fishes appear to be an excellent group of organisms for studying sex chromosome evolution and differentiation in vertebrates because they show considerable variability in the mechanisms and (or) patterns involved in sex determination.     

Complexities of chromosome landing in a highly duplicated genome: toward map-based cloning of a gene controlling blackleg resistance in Brassica napus

The LmR1 locus, which controls seedling resistance to the blackleg fungus Leptosphaeria maculans in the Brassica napus cultivar Shiralee, was positioned on linkage group N7. Fine genetic mapping in a population of 2500 backcross lines identified three molecular markers that cosegregated with LmR1. Additional linkage mapping in a second population colocalized a seedling resistance gene, ClmR1, from the cultivar Cresor to the same genetic interval on N7 as LmR1. Both genes were located in a region that showed extensive inter- and intragenomic duplications as well as intrachromosomal tandem duplications. The tandem duplications seem to have occurred in the Brassica lineage before the divergence of B. rapa and B. oleracea but after the separation of Brassica and Arabidopsis from a common ancestor. Microsynteny was found between the region on N7 carrying the resistance gene and the end of Arabidopsis chromosome 1, interrupted by a single inversion close to the resistance locus. The collinear region in Arabidopsis was assayed for the presence of possible candidate genes for blackleg resistance. These data provided novel insights into the genomic structure and evolution of plant resistance loci and an evaluation of the candidate gene approach using comparative mapping with a model organism.     

Mapping of sex determination loci on the white campion (Silene latifolia) Y chromosome using amplified fragment length polymorphism

S. latifolia is a dioecious plant with morphologically distinct sex chromosomes. To genetically map the sex determination loci on the male-specific Y chromosome, we identified X-ray-induced sex determination mutants that had lost male traits. We used male-specific AFLP markers to characterize the extent of deletions in the Y chromosomes of the mutants. We then compared overlapping deletions to predict the order of the AFLP markers and to locate the mutated sex-determining genes. We found three regions on the Y chromosome where frequent deletions were significantly associated with loss of male traits. One was associated with hermaphroditic mutants. A second was associated with asexual mutants that lack genes needed for early stamen development and a third was associated with asexual mutants that lack genes for late stages of stamen development. Our observations confirmed a classical genetic prediction that S. latifolia has three dispersed male-determining loci on the Y chromosome, one for carpel suppression, one for early stamen development, and another for late stamen development. This AFLP map provides a framework for locating genes on the Y chromosome and for characterizing deletions on the Y chromosomes of potentially interesting mutants.     

Genetic basis of cross-resistance to three organophosphate insecticides in Drosophila melanogaster (Diptera: Drosophilidae)

To investigate the genetic basis of cross-resistance to insecticides, we conducted genetic analyses of resistance to three organophosphate insecticides, malathion, prothiophos, and fenitrothion. After isofemale lines resistant and susceptible to all of the three organophosphates had been screened from natural populations of Drosophila melanogaster (Meigen), chromosomal analyses were performed by using chromosome-substituted lines between the resistant and the susceptible lines. The chromosomal analyses revealed that both the second and the third chromosomes contributed to resistance to the organophosphates, suggesting that this resistant line possessed at least two factors for organophosphate resistance. However, the relative contribution of each chromosome was different in resistance to different organophosphates. We further carried out genetic mapping of a resistance factor for each organophosphate on each of the two chromosomes. Each resistance factor was mapped to the position of each chromosome, about II-62 and III-50. Results of the chromosomal analyses and the genetic mapping revealed that at least two resistance factors exhibiting different patterns of cross-resistance to the organophosphates existed within a natural population of D. melanogaster. Based on this research, genetic variation in insecticide resistance within natural populations and complex as well as simple aspects of the mechanism of cross-resistance are discussed.     

Heterochiasmy and the establishment of gsdf as a novel sex determining gene in Atlantic halibut

Atlantic Halibut (Hippoglossus hippoglossus) has a X/Y genetic sex determination system, but the sex determining factor is not known. We produced a high-quality genome assembly from a male and identified parts of chromosome 13 as the Y chromosome due to sequence divergence between sexes and segregation of sex genotypes in pedigrees. Linkage analysis revealed that all chromosomes exhibit heterochiasmy, i.e. male-only and female-only meiotic recombination regions (MRR/FRR). We show that FRR/MRR intervals differ in nucleotide diversity and repeat class content and that this is true also for other Pleuronectidae species. We further show that remnants of a Gypsy-like transposable element insertion on chr13 promotes early male specific expression of gonadal somatic cell derived factor (gsdf). Less than 4.5 MYA, this male-determining element evolved on an autosomal FRR segment featuring pre-existing male meiotic recombination barriers, thereby creating a Y chromosome. Our findings indicate that heterochiasmy may facilitate the evolution of genetic sex determination systems relying on linkage of sexually antagonistic loci to a sex-determining factor.     

Linkage study on dieldrin resistance and an inversion on the second chromosome of Anopheles stephensi.

In a study on the linkage between the gene for dieldrin resistance and an inversion on the second chromosome in Anopheles stephensi, the two factors were found to assort independently. As dieldrin resistance can be assigned either to the third chromosome, or to a position on the second chromosome more than 50 cross-over units from the inversion.