scholarly journals Behaviour of Flanking Markers in Allelic Crosses

1966 ◽  
Vol 19 (6) ◽  
pp. 1047 ◽  
Author(s):  
DG Catcheside
Keyword(s):  
Fine Structure ◽  
Genetic Recombination ◽  
Genetic Differences ◽  
Quantitative Theory ◽  
Allelic Differences

The principles of analysis of the distributions of flanking markers amongst prototrophic recombinants arising from allelic auxotrophic differences are discussed. Considerable variations occur in the parameters which may be measured and also in the degree of agreement of criteria used to place allelic differences in order in fine structure maps. At least some of these variations appear likely to depend upon genetic differences affecting the mechanisms which result in genetic recombination and the mechanisms which control their activity. An approach to a quantitative theory of the distribution of flanking markers is suggested.

scholarly journals Division of Giardia isolates from humans into two genetically distinct assemblages by electrophoretic analysis of enzymes encoded at 27 loci and comparison with Giardia muris

Parasitology ◽  
1995 ◽  
Vol 111 (1) ◽  
pp. 11-17 ◽  
Author(s):  
G. Mayrhofer ◽  
R. H. Andrews ◽  
P. L. Ey ◽  
N. B. Chilton
Keyword(s):  
Homo Sapiens ◽  
Single Species ◽  
Electrophoretic Analysis ◽  
Genetic Differences ◽  
Giardia Intestinalis ◽  
Evolutionary Relationships ◽  
Enzyme Loci ◽  
Allelic Differences ◽  
Animal Hosts ◽  
Giardia Muris

SUMMARYGiardia that infect humans are known to be heterogeneous but they are assigned currently to a single species, Giardia intestinalis (syn. G. lamblia). The genetic differences that exist within G. intestinalis have not yet been assessed quantitatively and neither have they been compared in magnitude with those that exist between G. intestinalis and species that are morphologically similar (G. duodenalis) or morphologically distinct (e.g. G. muris). In this study, 60 Australian isolates of G. intestinalis were analysed electrophoretically at 27 enzyme loci and compared with G. muris and a feline isolate of G. duodenalis. Isolates of G. intestinalis were distinct genetically from both G. muris (approximately 80% fixed allelic differences) and the feline G. duodenalis isolate (approximately 75% fixed allelic differences). The G. intestinalis isolates were extremely heterogeneous but they fell into 2 major genetic assemblages, separated by fixed allelic differences at approximately 60% of loci examined. The magnitude of the genetic differences between the G. intestinalis assemblages approached the level that distinguished the G. duodenalis isolate from the morphologically distinct G. muris. This raises important questions about the evolutionary relationships of the assemblages with Homo sapiens, the possibility of ancient or contemporary transmission from animal hosts to humans and the biogeographical origins of the two clusters.

Electrophoretic contributions to the systematics of the freshwater crayfish genus Engaeus Erichson (Decapoda : Parastacidae)

1990 ◽  
Vol 4 (3) ◽  
pp. 615 ◽  
Author(s):  
P Horwitz ◽  
M Adams ◽  
P Baverstock
Keyword(s):  
Allelic Variation ◽  
Threshold Level ◽  
Sympatric Species ◽  
Biological Species ◽  
Genetic Differences ◽  
Freshwater Crayfish ◽  
Electrophoretic Data ◽  
Allelic Differences ◽  
Low Levels ◽  
Group Relationships

As part of an examination into the systematics of the freshwater crayfish genus Engaeus, an electrophoretic evaluation of specimens from a large number of collecting sites has been undertaken. From a total of 76 sample sets, a minimum of 30 distinct biological species have been delineated. Strong evidence from sites of both sympatry and allopatry suggests some further delineations of species but these must await additional discriminatory information. Sympatric species were detected on 11 separate occasions. In each case, fixed allelic differences were found, indicating an absence of interbreeding between each sympatric pair. Allopatric species were delineated where genetic differences between populations exceeded a threshold level determined from observed genetic differences between sympatric Engaeus species and between other (mainly decapod) species in the literature. The results of this analysis have confirmed low levels of heterozygosity in Engaeus species. Frequent isoIation of small populations of Engaeus species, and consequent loss of allelic variation, is suggested as a possible cause of these low levels. Some species have shown variation of allelic frequencies over their geographical range and, in some cases, this variation could be interpreted as showing clinal properties. Finally, the electrophoretic data have been interpreted to produce some information regarding the phylogenetic affinities of delineated species. Several groups of species were found which shared closer intra-group relationships than they did to the other species of Engaeus.

scholarly journals THE Ah LOCUS: BIOCHEMICAL BASIS FOR GENETIC DIFFERENCES IN BRAIN TUMOR FORMATION IN MICE

Genetics ◽  
1979 ◽  
Vol 92 (4) ◽  
pp. 1205-1210
Author(s):  
Roy C Levitt ◽  
Jacquelene M Fysh ◽  
Nancy M Jensen ◽  
Daniel W Nebert
Keyword(s):  
Inbred Mouse ◽  
Inbred Mouse Strain ◽  
Strain Differences ◽  
Tumor Formation ◽  
Genetic Differences ◽  
Polycyclic Hydrocarbon ◽  
Intracranial Neoplasms ◽  
Biochemical Basis ◽  
Allelic Differences ◽  
The Brain

ABSTRACT Allelic differences at the Ah locus are shown to exist in the mouse brain. This finding probably explains inbred mouse strain differences in polycyclic hydrocarbon tumorigenesis of the brain described more than 35 years ago and may be important in understanding the etiology of genetic differences in certain human intracranial neoplasms.

HOMOLOGOUS RECOMBINATION BETWEEN EPISOMAL PLASMIDS AND CHROMOSOMES IN YEAST

Genetics ◽  
1983 ◽  
Vol 105 (4) ◽  
pp. 843-856
Author(s):  
S Carl Falco ◽  
Mark Rose ◽  
David Botstein
Keyword(s):  
Fine Structure ◽  
Homologous Recombination ◽  
Genetic Recombination ◽  
Recombination Frequency ◽  
Mitotic Recombination ◽  
Base Pairs ◽  
The Third ◽  
Chromosome Recombination ◽  
Gene Conversions ◽  
Double Crossovers

ABSTRACT We have observed genetic recombination between ura3  - mutations (among them extensive deletions) carried on "episomal" (i.e., 2μ DNA-containing) plasmids and other ura3  - alleles present at the normal chromosomal URA3 locus. The recombination frequency found was comparable to the level observed for classical mitotic recombination but was relatively insensitive to sunlamp radiation, which strongly stimulates mitotic recombination. Three equally frequent classes could be distinguished among the recombinants. Two of these are the apparent result of gene conversions (or double crossovers) which leave the URA3  + allele on the chromosome (class I) or on the plasmid (class II). The third class is apparently due to a single crossover that results in the integration of the plasmid into a chromosome. Plasmid-chromosome recombination can be useful in fine structure genetic mapping, since recombination between a chromosomal point mutation and a plasmid-borne deletion mutation only 25 base pairs distant was easily detected.

Selection of specific genotypes ofgiardia intestinalisby growthin vitroandin vivo

Parasitology ◽  
1992 ◽  
Vol 105 (3) ◽  
pp. 375-386 ◽  
Author(s):  
R. H. Andrews ◽  
N. B. Chilton ◽  
G. Mayrhofer
Keyword(s):  
Growth Conditions ◽  
Genetic Differences ◽  
Clinical Isolates ◽  
Suckling Mice ◽  
Allelic Differences ◽  
Gene Switching ◽  
Selection Of ◽  
Made In

SUMMARYThis study examined whether allelic changes observed when clinical isolates ofGiardia intestinalismade in suckling mice were adapted toin vitrogrowth occurred as a result of gene switching (alternate isoenzymes) or through selection of organisms with different genotypes from mixed infections. Samples were compared electrophoretically at 20 enzyme loci. Marked allelic differences were detected between the uncloned clinical isolates grown in mice and the axenic cultures established from them. Furthermore, the allelic profiles of the uncloned isolates changed during the course ofin vivoorin vitrogrowth. In contrast, all clones produced from each isolate retained identical allelic profiles, regardless of whether they were grownin vivoorin vitro. These findings argue against gene switching as an explanation for the observed allozyme changes and support preferential selection of organisms with specific genotypes by growth conditions. The data indicate the presence of at least 2 and possibly up to 4 distinct genotypes within each clinical isolate. The genetic differences detected between clinical isolates in suckling mice were of similar magnitude to those that separate different axenic isolates ofG. intestinalisinto cryptic species. Conversely, the genetic differences between the isolates were limited when sampled after establishmentin vitro. These findings have significant implications for research onGiardiaand other medically important parasites and raise the possibility that culture may exert a similar selective bias on the genotypes isolated from infections with other parasitic protozoa.

Apparent absence of genetic differences among species of Teladorsagia (Nematoda: Trichostrongylidae)

1990 ◽  
Vol 64 (4) ◽  
pp. 290-294 ◽  
Author(s):  
R. H. Andrews ◽  
I. Beveridge
Keyword(s):  
Genetic Variation ◽  
Genetic Data ◽  
Single Species ◽  
Genetic Differences ◽  
Morphological Evidence ◽  
Allozyme Electrophoresis ◽  
Apparent Absence ◽  
Enzyme Loci ◽  
Data Support ◽  
Allelic Differences

ABSTRACTThe technique of allozyme electrophoresis was applied to three species of Teladorsagia present in sheep to determine the extent of genetic variation among species. Thirty-four enzyme loci were established of which 22 were invariant and 12 were shown to be polymorphic. No fixed allelic differences were detected among the species and the level of polymorphism was within the range found commonly between populations of a single species. Therefore, the genetic data support breeding data and existing morphological evidence that T. circumcincta, T. davtiani and T. trifurcata as currently recognized do in fact belong to a single species.

scholarly journals Genetic changes are introduced by repeated exposure of Salmonella spiked in low water activity and high fat matrix to heat

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Leen Baert ◽  
Johan Gimonet ◽  
Caroline Barretto ◽  
Coralie Fournier ◽  
Balamurugan Jagadeesan
Keyword(s):  
Water Activity ◽  
Genetic Differences ◽  
Mutation Rates ◽  
Source Tracking ◽  
High Fat ◽  
Genetic Changes ◽  
Root Cause ◽  
Allelic Differences ◽  
Outbreak Investigations ◽  
Contamination Event

AbstractWGS is used to define if isolates are “in” or “out” of an outbreak and/or microbial root cause investigation. No threshold of genetic differences is fixed and the conclusions on similarity between isolates are mainly based on the knowledge generated from previous outbreak investigations and reported mutation rates. Mutation rates in Salmonella when exposed to food processing conditions are lacking. Thus, in this study, the ability of heat and dry stress to cause genetic changes in two Salmonella serotypes frequently isolated from low moisture foods was investigated. S. enterica serovars S. Agona ATCC 51,957 and S. Mbandaka NCTC 7892 (ATCC 51,958) were repeatedly exposed to heat (90 °C for 5 min) in a low water activity and high fat matrix. No increased fitness of the strains was observed after 10 repeated heat treatments. However, genetic changes were introduced and the number of genetic differences increased with every heat treatment cycle. The genetic changes appeared randomly in the genome and were responsible for a population of diverse isolates with 0 to 28 allelic differences (0 to 38 SNPs) between them. This knowledge is key to interpret WGS results for source tracking investigations as part of a root cause analysis in a contamination event as isolates are exposed to stress conditions.

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