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At least 595 records · Page 33Linked to original sources
PubMed1994

Genetic variability of the beta-tubulin genes in benzimidazole-susceptible and -resistant strains of Haemonchus contortus.

Benzimidazole anthelmintics are the most common chemotherapeutic agents used to remove intestinal helminths from farm animals. The development of drug resistance within helminth populations is wide-spread and can render these drugs essentially useless. The mechanism of benzimidazole resistance appears to be common to many species ranging from fungi to nematodes and involves alterations in the genes encoding beta-tubulin. During the selection process resulting in resistance, there must be quantitative changes in the population gene pool. Knowledge of these changes would indicate the mechanisms underlying the spread of resistance in the population, which in turn could be used to design more effective drug administration strategies. To this end we have identified allelic variation at two beta-tubulin genes in Haemonchus contortus using restriction map analysis of individual adults. Extremely high levels of variation were identified at both loci within a susceptible strain. In two independently derived benzimidazole resistant strains, allele frequencies at both loci were significantly different from the susceptible strain but not from each other. The same alleles at both loci, in both resistant strains, were favored by selection with benzimidazoles, suggesting that both loci are involved in determining benzimidazole resistance. These data confirm that changes in allele frequency, rather than novel genetic rearrangements induced by exposure to the drug, explain the changes associated with benzimidazole resistance. These results also show that any DNA based test for the development of benzimidazole resistance must take into account the frequency of alleles present in the population and not simply test for the presence or absence of specific allelic types.

Alleles↗
PubMed1977

Genetic markers in Libyan Jews.

Blood groups, serum proteins, and red-cell enzyme frequencies were determined on a random sample of 148 Libyan Jews now settled in Israel. Comparisons with data on Libyan non-Jews show significant differences in most systems, implying maintenance of a high degree of genetic isolation of the Jewish group from surrounding populations. The relative lack of the African component in their gene pool shows that they have interbred very little, if at all, with their negroid neighbours.

Blood Group Antigens↗
PubMed2003

Genetic variation among interconnected populations of Catostomus occidentalis: implications for distinguishing impacts of contaminants from biogeographical structuring.

Exposure to contaminants can affect survivorship, recruitment, reproductive success, mutation rates and migration, and may play a significant role in the partitioning of genetic variation among exposed and nonexposed populations. However, the application of molecular population genetic data to evaluate such influences has been uncommon and often flawed. We tested whether patterns of genetic variation among native fish populations (Sacramento sucker, Catostomus occidentalis) in the Central Valley of California were consistent with long-term pesticide exposure history, or primarily with expectations based on biogeography. Field sampling was designed to rigorously test for both geographical and contamination influences. Fine-scale structure of these interconnected populations was detected with both amplified fragment length polymorphisms (AFLP) and microsatellite markers, and patterns of variation elucidated by the two marker systems were highly concordant. Analyses indicated that biogeographical hypotheses described the data set better than hypotheses relating to common historical pesticide exposure. Downstream populations had higher genetic diversity than upstream populations, regardless of exposure history, and genetic distances showed that populations from the same river system tended to cluster together. Relatedness among populations reflected primarily directions of gene flow, rather than convergence among contaminant-exposed populations. Watershed geography accounted for significant partitioning of genetic variation among populations, whereas contaminant exposure history did not. Genetic patterns indicating contaminant-induced selection, increased mutation rates or recent bottlenecks were weak or absent. We stress the importance of testing contaminant-induced genetic change hypotheses within a biogeographical context. Strategic application of molecular markers for analysis of fine-scale structure, and for evaluating contaminant impacts on gene pools, is discussed.

Analysis of Variance↗
PubMed1977

The genetic control of the immune response to staphylococcal nuclease VI. Recombination between genes determining the A/J anti-nuclease idiotypes and the heavy chain allotype locus.

Rat antisera detecting binding site-specific idiotypic determinants on anti-nuclease antibodies from A/J mice have been used to define the A/J anti-nuclease idiotype and to investigate its genetic linkage as a variable region marker. Analysis of the segregation of the A/J idiotype in progeny of the backcross (B10.A X A/J) X B10.A showed linkage of the idiotype to the Ig-1e heavy chain allotype locus. There was, however, a very high apparent frequency of recombination, with 7 of 101 backcross animals having a recombinant phenotype. All of these putative recombinants were accounted for by Ig-1b/Ig-1b homozygotes which bore the A/J idiotype, and none by Ig-1b/Ig-1e heterozygotes lacking the idiotype. On progeny testing of these animals in another backcross to B10.A the recombinant trait bred true. If this idiotype is indeed a marker for variable region structural genes, then the germ line gene pool must be very large or there must be special genetic mechanism to account for the increased recombinational frequency observed.

Animals↗
PubMed1992

Huntington's disease in Chinese: a hypothesis of its origin.

The period prevalence (1984-91) of Huntington's disease (HD) in Hong Kong Chinese was 3.7 per million population. HD patients in Mainland China and Hong Kong showed similar hereditary pattern, clinical and pathological features as in the West. Chinese HD patients were male predominant with a younger age of onset and death. Their ancestral origin could be traced mostly to the coastal provinces of China. It is proposed that Chinese HD patients may have a European origin and share the same gene pool as their white counterparts.

China↗
PubMedDate not supplied

Low frequency of isozyme 2 acid a-glucosidase in Greece.

The isozyme type 2 of acid a-glucosidase, identified by "affinity" starch gel electrophoresis, was found to have a gene frequency of 0.001 in an unselected Greek population from Southwestern Greece. The estimated frequency of the heterozygote in the population is 1 in 500 and of type 2 homozygote 10(-6). This frequency is by far lower than that reported in Europeans and other populations. This may be a characteristic of the Greek gene pool at the acid a-glucosidase locus or it may be present in populations of neighbouring countries as well.

Alleles↗
PubMed2005

Genome-wide introgression lines and their use in genetic and molecular dissection of complex phenotypes in rice (Oryza sativa L.).

Tremendous efforts have been taken worldwide to develop genome-wide genetic stocks for rice functional genomic (FG) research since the rice genome was completely sequenced. To facilitate FG research of complex polygenic phenotypes in rice, we report the development of over 20,000 introgression lines (ILs) in three elite rice genetic backgrounds for a wide range of complex traits, including resistances/tolerances to many biotic and abiotic stresses, morpho-agronomic traits, physiological traits, etc., by selective introgression. ILs within each genetic background are phenotypically similar to their recurrent parent but each carries one or a few traits introgressed from a known donor. Together, these ILs contain a significant portion of loci affecting the selected complex phenotypes at which allelic diversity exists in the primary gene pool of rice. A forward genetics strategy was proposed and demonstrated with examples on how to use these ILs for large-scale FG research. Complementary to the genome-wide insertional mutants, these ILs opens a new way for highly efficient discovery, candidate gene identification and cloning of important QTLs for specific phenotypes based on convergent evidence from QTL position, expression profiling, functional and molecular diversity analyses of candidate genes, highlights the importance of genetic networks underlying complex phenotypes in rice that may ultimately lead to more complete understanding of the genetic and molecular bases of quantitative trait variation in rice.

Adaptation, Physiological↗
PubMed2005

Bacterial populations active in metabolism of C1 compounds in the sediment of Lake Washington, a freshwater lake.

Active members of the bacterial community in the sediment of Lake Washington, with special emphasis on C1 utilizers, were identified by employing two complementary culture-independent approaches: reverse transcription of environmental mRNA and 16S rRNA combined with PCR (RT-PCR) and stable-isotope probing (SIP) of DNA with the 13C-labeled C1 substrates methanol, methylamine, formaldehyde, and formate. Analysis of RT-PCR-amplified fragments of 16S rRNA-encoding genes revealed that gammaproteobacterial methanotrophs belonging to Methylobacter and Methylomonas dominate the active methylotroph population, while only one other known methylotrophic lineage, Methylophilaceae, was detected via this approach. Analysis of RT-PCR-amplified functional genes, pmoA and fae, allowed detection of alphaproteobacterial (Methylosinus) and gammaproteobacterial (Methylobacter, Methylomonas, and Methylomicrobium) methanotrophs, methylotrophs of the genus Methylobacterium, and yet-unidentified proteobacteria. SIP experiments allowed detection of a broad variety of groups actively metabolizing C1 compounds. Comparisons between 16S rRNA gene pools amplified from [13C]DNA and from [12C]DNA revealed that the proportion of Methylophilus-related sequences increased in the presence of [13C]methanol, [13C]methylamine, and [13C]formaldehyde; Novosphingobium-related sequences were enriched in the presence of [13C]methanol; Gemmatimonadaceae-related sequences were enriched in the presence of [13C]formaldehyde and [13C]formate; and Xanthomonadaceae-related sequences were enriched in the presence of [13C]formate. Analysis of fae genes amplified from [13C]DNAs isolated from different microcosms revealed specific shifts in populations in response to a specific C1 compound: Methylosinus sequences dominated the [13C]methanol microcosm pool, and beta- and gammaproteobacterial sequences dominated the [13C]methylamine microcosm pool. The [13C]formaldehyde microcosm was dominated by betaproteobacterial sequences and by sequences of a nonaffiliated group, while the [13C]formate microcosm was dominated by alpha- and betaproteobacterial sequences. Overall, these data point toward the presence of a diverse population of active methylotrophs in Lake Washington sediments and toward the existence of yet-uncultivated organisms.

Bacterial Proteins↗
PubMed1991

Restriction fragment length polymorphism in plants and its implications.

In the last decade RFLP analysis has evolved from an idea that seemed promising to a well-established tool that has led to fundamental advances in several fields. Construction of genetic maps has now become feasible in many organisms where it would previously have been impractical. Since genetic maps are of general utility for many sorts of biological research, they cannot fail to have a significant impact in the immediate future. As genetic maps become reconciled with physical maps in several plants, it will become possible to clone virtually any gene. For a plant breeder this will have the effect of broadening the gene pool available for plant improvement to include virtually all organisms, including animals and microorganisms. Much remains to be done, however. We need basic studies of the biochemistry, physiology, and genetics of plants and the insects and pathogens infesting them to be able to identify target genes for cloning. We need basic studies of transformation and gene expression to be able to have introduced genes expressed in transformed plants in the proper amounts and in the desired tissues. It must also be kept in mind that the best of our present technologies only suffice to clone and transform single genes. We will have to make another large jump in capabilities to be able to transfer QTL between plants. Since the most important agronomic traits are controlled by QTL, this effort will have to be undertaken. However, the future looks promising for plant breeding and RFLP analysis. The molecular genetic revolution now has every indication of being transferrable to practical problems such as plant breeding, and the first steps in this transferral have already occurred through the medium of RFLP analysis.

Breeding↗
PubMed1999

Frequency of the CCR5 gene 32-basepair deletion in Hispanic Mexicans.

A 32-basepair deletion polymorphism in the CCR5 chemokine receptor gene (DeltaCCR5) has recently been identified and shown to have functional significance in determining susceptibility to infection by human immunodeficiency virus type 1 (HIV-1) and a possible influence on disease progression in HIV-1-positive individuals. Interest has also focused on the geographical distribution of the DeltaCCR5 allele, particularly in considering epidemiological aspects of HIV disease and its impact on health economics. In this report we have assessed the frequency of the DeltaCCR5 allele in a Hispanic Mexican population and found a gene frequency of 4.4% in 103 individuals. The DeltaCCR5 allele is not present in indigenous Mexican populations but is present in about 8% of the population in Spain. Gene flow from the European gene pool consistent with Mexico's colonial past would account for the findings in this study.

Alleles↗
PubMed1993

Nucleotide sequence comparison of the VP8* gene of rotaviruses possessing the AU-1 gene 4 allele.

Of the five currently recognized alleles of the human rotavirus VP4 gene, the AU-1 allele has captured attention because of its possible non-human origin. The 5' 750 nucleotide region of the VP4 gene, encoding the VP8* fragment [amino acids (aa) 1 to 241] and the connecting peptide (aa 242 to 247), from 13 human and two feline rotavirus strains possessing the AU-1 allele was highly conserved both at the nucleotide sequence (93.8 to 99.7% identity) and amino acid level (95.5 to 100% identity) irrespective of the year and the place of isolation or of the host species from which these viruses were isolated. This is consistent with the hypothesis that the AU-1 allele of the VP4 gene has been maintained in both human and feline rotavirus gene pools.

Alleles↗
PubMedDate not supplied

[Immunogenetic structure of the Ukrainian White Steppe species pig herd by frequency of complex genotypes in connection with some parameters of productivity].

Studying of the structural organization of the gene pool considering frequencies of occurrence of complex genotypes in animals simultaneously by many loci of blood groups allows to better characterize immunogenetic parameters of populations and peculiarities of selection acting upon animals of different genetic classes. The data on presence of the optimum level of gene diversity and peculiarities of selection acting upon polymorphic systems of blood groups in the pig herd of Ukrainian Steppe White breed have been obtained. The results can be used for increasing efficiency of breeding.

Animal Husbandry↗
PubMed1995

Mitochondrial and nuclear genetic contribution of female founders to a contemporary population in northeast Quebec.

A common challenge in population genetics is to reconstruct the evolutionary history of populations on the basis of current allele frequencies. Through pedigree analysis, we have the opportunity to study the genetic contribution of founders to the contemporary population. This contribution over many generations accounts for the probable introduction, survival, and extinction of genes in the population. I use this method to follow nuclear and mitochondrial genes in the Saguenay population of northeast Quebec by tracing back ascending genealogies of 160,315 individuals born between 1950 and 1971 by using the BALSAC database. This study leads us to conclude that even in a growing population, the loss rate of mtDNA is high. The survival of mtDNA in the population is independent of the time of introduction in the population. The number of copies of a particular mtDNA gene in the contemporary population is higher for genes introduced earlier, but the correlation between these two variables is low (the relation is not linear). Compared to nuclear contribution, mitochondrial contribution is higher, but the loss rate of nuclear DNA is lower. The differential contribution (the fact that few founders contribute a lot) is the same proportion for nuclear and mtDNA, but only 592 female founders contribute 50% of the mtDNA gene pool of the contemporary cohort, compared to 994 for nuclear DNA. Since we have no molecular data on founders' haplotypes, these results cannot give us the diversity level in the population. However, this study enables us to compare the evolutionary fates of nuclear and mitochondrial genes in this expanding population.

Biological Evolution↗
PubMed2006

Hybridization of Bombina bombina and B. variegata (Anura, Discoglossidae) at a sharp ecotone in western Ukraine: comparisons across transects and over time.

Bombina bombina and B. variegata are two anciently diverged toad taxa that have adapted to different breeding habitats yet hybridize freely in zones of overlap where their parapatric distributions meet. Here, we report on a joint genetic and ecological analysis of a hybrid zone in the vicinity of Stryi in western Ukraine. We used five unlinked allozyme loci, two nuclear single nucleotide polymorphisms and a mitochondrial DNA haplotype as genetic markers. Parallel allele frequency clines with a sharp central step occur across a sharp ecotone, where transitions in aquatic habitat, elevation, and terrestrial vegetation coincide. The width of the hybrid zone, estimated as the inverse of the maximum gradient in allele frequency, is 2.3 km. This is the smallest of four estimates derived from different clinal transects across Europe. We argue that the narrow cline near Stryi is mainly due to a combination of habitat distribution and habitat preference. Adult toads show a preference for either ponds (B. bombina) or puddles (B. variegata), which is known to affect the distribution of genotypes within the hybrid zones. At Stryi, it should cause a reduction of the dispersal rate across the ecotone and thus narrow the cline. A detailed comparison of all five intensively studied Bombina transects lends support to the hypothesis that habitat distribution plus habitat preference can jointly affect the structure of hybrid zones and, ultimately, the resulting barriers to gene flow between differentiated gene pools. This study also represents a resampling of an area that was last studied more than 70 years ago. Our allele-frequency clines largely coincide with those that were described then on the basis of morphological variation. However, we found asymmetrical introgression of B. variegata genes into B. bombina territory along the bank of a river.

Animals↗
PubMed2005

Antibiotic resistance of bacteria in raw and biologically treated sewage and in groundwater below leaking sewers.

More than 750 isolates of faecal coliforms (>200 strains), enterococci (>200 strains) and pseudomonads (>340 strains) from three wastewater treatment plants (WTPs) and from four groundwater wells in the vicinity of leaking sewers were tested for resistance against 14 antibiotics. Most, or at least some, strains of the three bacterial groups, isolated from raw or treated sewage of the three WTPs, were resistant against penicillin G, ampicillin, vancomycin, erythromycin, triple sulfa and trimethoprim/sulfamethoxazole (SXT). Only a few strains of pseudomonads or faecal coliforms were resistant against some of the other tested antibiotics. The antibiotic resistances of pseudomonads, faecal coliforms and enterococci from groundwater varied to a higher extent. In contrast to the faecal coliforms and enterococci, most pseudomonads from all groundwater samples, including those from non-polluted groundwater, were additionally resistant against chloramphenicol and SXT. Pseudomonads from sewage and groundwater had more multiple antibiotic resistances than the faecal coliforms or the enterococci, and many pseudomonads from groundwater were resistant to more antibiotics than those from sewage. The pseudomonads from non-polluted groundwater were the most resistant isolates of all. The few surviving faecal coliforms in groundwater seemed to gain multiple antibiotic resistances, whereas the enterococci lost antibiotic resistances. Pseudomonads, and presumably, other autochthonous soil or groundwater bacteria, such as antibiotic-producing Actinomyces sp., seem to contribute significantly to the gene pool for acquisition of resistances against antibiotics in these environments.

Actinobacteria↗
PubMed2006

Phylogenetic relationships among indigenous sheep populations in East Asia based on five informative blood protein and nonprotein polymorphisms.

The phylogenetic relationships among 23 local sheep breeds and varieties in East Asia were determined based on allele frequency data for five informative and polymorphic blood protein and nonprotein loci (transferrin, arylesterase, hemoglobin-beta, X-protein, and potassium transport) using electrophoresis and ion-densitometric techniques. Comparatively striking differences in the frequency distributions, especially of hemoglobin-beta and X-protein alleles, were seen between the northern population of the Khalkhas, Bhyanglung, Baruwal, Jakar, Sakten, and five Chinese breeds and the southern population of the Bengal, Kagi, Lampuchhre, Myanmar, and Sipsu breeds. Clustering analyses using UPGMA and NJ methods and principal component analysis, using the data of all populations and loci tested, clearly demonstrated the difference. The two population groups are divided by the boundary of the Himalayas, and each diverged into three subgroups: Mongolian, Tibetan, and Himalayan groups in the north and Indian groups I, II, and III in the south. It was noted that the genetic differentiation of populations was more distinct in the northern group. These findings strongly suggest the existence of at least two large and phylogenetically different gene pools of sheep in East Asia.

Animals↗
PubMed1989

Identification of the structural mutation responsible for the dibucaine-resistant (atypical) variant form of human serum cholinesterase.

A point mutation in the gene for human serum cholinesterase was identified that changes Asp-70 to Gly in the atypical form of serum cholinesterase. The mutation in nucleotide 209, which changes codon 70 from GAT to GGT, was found by sequencing a genomic clone and sequencing selected regions of DNA amplified by the polymerase chain reaction. The entire coding sequences for usual and atypical cholinesterases were compared, and no other consistent base differences were found. A polymorphic site near the C terminus of the coded region was detected, but neither allele at this locus segregated consistently with the atypical trait. The nucleotide-209 mutation was detected in all five atypical cholinesterase families examined. There was complete concordance between this mutation and serum cholinesterase phenotypes for all 14 heterozygous and 6 homozygous atypical subjects tested. The mutation causes the loss of a Sau3A1 restriction site; the resulting DNA fragment length polymorphism was verified by electrophoresis of 32P-labeled DNA restriction fragments from usual and atypical subjects. Dot-blot hybridization analysis with a 19-mer allele-specific probe to the DNA amplified by the polymerase chain reaction distinguished between the usual and atypical genotypes. We conclude that the Asp-70----Gly mutation (acidic to neutral amino acid substitution) accounts for reduced affinity of atypical cholinesterase for choline esters and that Asp-70 must be an important component of the anionic site. Heterogeneity in atypical alleles may exist, but the Asp-70 point mutation may represent an appreciable portion of the atypical gene pool.

Base Sequence↗
PubMed2006

Molecular characterization of a diagnostic DNA marker for domesticated tetraploid wheat provides evidence for gene flow from wild tetraploid wheat to hexaploid wheat.

All forms of domesticated tetraploid wheat (Triticum turgidum, genomes AABB) are nearly monomorphic for restriction fragment length polymorphism (RFLP) haplotype a at the Xpsr920 locus on chromosome 4A (Xpsr920-A1a), and wild tetraploid wheat is monomorphic for haplotype b. The Xpsr920-A1a/b dimorphism provides a molecular marker for domesticated and wild tetraploid wheat, respectively. Hexaploid wheat (Triticum aestivum, genomes AABBDD) is polymorphic for the 2 haplotypes. Bacterial artificial chromosome (BAC) clones hybridizing with PSR920 were isolated from Triticum urartu (genomes AA), Triticum monococcum (genomes AmAm), and T. turgidum ssp. durum (genomes AABB) and sequenced. PSR920 is a fragment of a putative ATP binding cassette (ABC) transporter gene (designated ABCT-1). The wheat ABCT-1 gene is more similar to the T. urartu gene than to the T. monococcum gene and diverged from the T. urartu gene about 0.7 MYA. The comparison of the sequence of the wheat A genome BAC clone with that of the T. urartu BAC clone provides the first insight into the microsynteny of the wheat A genome with that of T. urartu. Within 103 kb of orthologous intergenic space, 37 kb of new DNA has been inserted and 36 kb deleted leaving 49.7% of the region syntenic between the clones. The nucleotide substitution rate in the syntenic intergenic space has been 1.6 x 10(-8) nt(-1) year(-1), which is, respectively, 4 and 3 times as great as nucleotide substitution rates in the introns and the third codon positions of the juxtaposed gene. The RFLP is caused by a miniature inverted transposable element (MITE) insertion into intron 18 of the ABCT-A1 gene. Polymerase chain reaction primers were developed for the amplification of the MITE insertion site and its sequencing. The T. aestivum ABCT-A1a haplotype is identical to the haplotype of domesticated tetraploid wheat, and the ABCT-A1b haplotype is identical to that of wild tetraploid wheat. This finding shows for the first time that wild tetraploid wheat participated in the evolution of hexaploid wheat. A cline of the 2 haplotype frequencies exists across Euro-Asia in T. aestivum. It is suggested that T. aestivum in eastern Asia conserved the gene pool of the original T. aestivum more than wheat elsewhere.

Chromosomes, Plant↗