scholarly journals ROLE OF DNA SEQUENCES IN GENETIC RECOMBINATION IN THE ISO-1-CYTOCHROME c GENE OF YEAST. I. DISCREPANCIES BETWEEN PHYSICAL DISTANCES AND GENETIC DISTANCES DETERMINED BY FIVE MAPPING PROCEDURES

Genetics ◽  
1975 ◽  
Vol 79 (3) ◽  
pp. 397-418
Author(s):  
Carol W Moore ◽  
Fred Sherman
Keyword(s):  
Ultraviolet Light ◽  
Dna Sequences ◽  
Meiotic Recombination ◽  
Genetic Recombination ◽  
Genetic Distances ◽  
Nucleotide Sequences ◽  
X Rays ◽  
Recombination Rates ◽  
Near Ultraviolet ◽  
X Irradiation

ABSTRACT Recombination rates have been examined in two-point crosses of various defined cyc1 mutants using five mapping methods. Nucleotide sequences of mutant codons were identified in previous studies from alterations in functional iso-1-cytochromes c produced by intragenic revertants. Heteroallelic diploids were analyzed for rates of mitotic recombination that occurred spontaneously and that were induced with X-rays, ultraviolet light and the near-ultraviolet light emitted by sunlamps, as well as rates of meiotic recombination that occur after sporulation. Frequencies of both mitotic and meiotic recombination do not necessarily correspond with physical distances separating altered nucleotides. The most extreme discrepancy involved two adjacent intervals of thirteen base pairs which differed approximately thirtyfold in their spontaneous and X-ray-induced recombination rates. Marked disproportions between genetic and physical distances appear to be due to the interaction of the two nucleotide sequences in the heteroallelic combination and not to the sequences of the mutant codons alone. Recombination values that were obtained by all five methods could not be used to establish the correct order of mutant sites. Relationships of the recombination rates for the various pairwise crosses are different after mitosis from those after meiosis, suggesting that these two recombinational processes are to some extent different in their dependence on particular nucleotide configurations. On the other hand, the relationships of the rates induced by UV-, sunlamp- and X-irradiation were identical or very similar. In addition to the intrinsic properties of the alleles affecting frequencies of mitotic and meiotic recombination rates, two- to threefold variations in recombination rates could be attributed to genetic backgrounds.

scholarly journals ROLE OF DNA SEQUENCES IN GENETIC RECOMBINATION IN THE ISO-1-CYTOCHROME c GENE OF YEAST. II. COMPARISON OF MUTANTS ALTERED AT THE SAME AND NEARBY BASE PAIRS

Genetics ◽  
1977 ◽  
Vol 85 (1) ◽  
pp. 1-22
Author(s):  
Carol W Moore ◽  
Fred Sherman
Keyword(s):  
Cytochrome C ◽  
Dna Sequences ◽  
Meiotic Recombination ◽  
Base Pair ◽  
Genetic Recombination ◽  
Initiation Codon ◽  
Recombination Rates ◽  
Base Pairs ◽  
Yeast Saccharomyces Cerevisiae ◽  
X Ray

ABSTRACT X-ray-induced mitotic recombination rates and spontaneous meiotic recombination rates have been determined in two-point crosses of various defined cyc1 mutants of the yeast Saccharomyces cerevisiae. All but one of the 17 cyc1 mutants chosen for this study contained either the addition, deletion or substitution of single base-pairs located within a defined segment of the gene that corresponds to the 11 amino acid residues at the amino terminus of iso-1-cytochrome c; approximately half of these mutants had alterations of the AUG initiation codon, some at the same base pair. Up to 66-fold differences in X-ray-induced recombination rates were observed when the same cyc1 mutant was crossed to cyc1 mutants having different alterations in the AUG initiation codon; over a ten-fold difference was observed in series of homologous crosses involving mutants with different changes at the same base-pair. Recombination rates that were associated with specific cyc1 mutants co-segregated with the particular alleles following meiosis, and comparable recombination patterns were also observed for independently isolated, identical mutations. With the mutants used in this study, the frequencies of meiotic recombination did not differ as markedly, suggesting a dissimilar dependence on specific DNA sequences for these two modes of recombination. These disproportionalities of recombination rates suggest that the nature of the mismatched bases influences the recombination process, but not in a way that can be simply interpreted.

scholarly journals Factors enforcing the species boundary between the human pathogens Cryptococcus neoformans and Cryptococcus deneoformans

PLoS Genetics ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. e1008871
Author(s):  
Shelby J. Priest ◽  
Marco A. Coelho ◽  
Verónica Mixão ◽  
Shelly Applen Clancey ◽  
Yitong Xu ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Mismatch Repair ◽  
Dna Sequences ◽  
Meiotic Recombination ◽  
Genetic Recombination ◽  
Species Boundaries ◽  
Repair System ◽  
Hybrid Progeny ◽  
Extant Species ◽  
Species Boundary

Hybridization has resulted in the origin and variation in extant species, and hybrids continue to arise despite pre- and post-zygotic barriers that limit their formation and evolutionary success. One important system that maintains species boundaries in prokaryotes and eukaryotes is the mismatch repair pathway, which blocks recombination between divergent DNA sequences. Previous studies illuminated the role of the mismatch repair component Msh2 in blocking genetic recombination between divergent DNA during meiosis. Loss of Msh2 results in increased interspecific genetic recombination in bacterial and yeast models, and increased viability of progeny derived from yeast hybrid crosses. Hybrid isolates of two pathogenic fungal Cryptococcus species, Cryptococcus neoformans and Cryptococcus deneoformans, are isolated regularly from both clinical and environmental sources. In the present study, we sought to determine if loss of Msh2 would relax the species boundary between C. neoformans and C. deneoformans. We found that crosses between these two species in which both parents lack Msh2 produced hybrid progeny with increased viability and high levels of aneuploidy. Whole-genome sequencing revealed few instances of recombination among hybrid progeny and did not identify increased levels of recombination in progeny derived from parents lacking Msh2. Several hybrid progeny produced structures associated with sexual reproduction when incubated alone on nutrient-rich medium in light, a novel phenotype in Cryptococcus. These findings represent a unique, unexpected case where rendering the mismatch repair system defective did not result in increased meiotic recombination across a species boundary. This suggests that alternative pathways or other mismatch repair components limit meiotic recombination between homeologous DNA and enforce species boundaries in the basidiomycete Cryptococcus species.

Meiotic recombination hotspots in plants

2006 ◽  
Vol 34 (4) ◽  
pp. 531-534 ◽  
Author(s):  
C. Mézard
Keyword(s):  
Plant Species ◽  
Meiotic Recombination ◽  
Large Scale ◽  
Genetic Recombination ◽  
Dna Fragments ◽  
Recombination Rates ◽  
Coding Regions ◽  
Recombination Hotspots ◽  
Meiotic Recombination Hotspots

Many studies have demonstrated that the distribution of meiotic crossover events along chromosomes is non-random in plants and other species with sexual reproduction. Large differences in recombination frequencies appear at several scales. On a large scale, regions of high and low rates of crossover have been found to alternate along the chromosomes in all plant species studied. High crossover rates have been reported to be correlated with several chromosome features (e.g. gene density and distance to the centromeres). However, most of these correlations cannot be extended to all plant species. Only a few plant species have been studied on a finer scale. Hotspots of meiotic recombination (i.e. DNA fragments of a few kilobases in length with a higher rate of recombination than the surrounding DNA) have been identified in maize and rice. Most of these hotspots are intragenic. In Arabidopsis thaliana, we have identified several DNA fragments (less than 5 kb in size) with genetic recombination rates at least 5 times higher than the whole-chromosome average [4.6 cM (centimorgan)/Mb], which are therefore probable hotspots for meiotic recombination. Most crossover breakpoints lie in intergenic or non-coding regions. Major efforts should be devoted to characterizing meiotic recombination at the molecular level, which should help to clarify the role of this process in genome evolution.

scholarly journals RESPONSE OF POTASSIUM RETENTIVITY AND SURVIVAL OF YEAST TO FAR-ULTRAVIOLET, NEAR-ULTRAVIOLET AND VISIBLE, AND X-RADIATION

1958 ◽  
Vol 41 (4) ◽  
pp. 693-702 ◽  
Author(s):  
A. K. Bruce
Keyword(s):  
Yeast Cell ◽  
Dose Response ◽  
X Rays ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Differential Effects ◽  
Near Ultraviolet ◽  
X Irradiation ◽  
Far Ultraviolet ◽  
Control Survival

Potassium retentivity and survival of yeast were studied after exposure to various kinds and conditions of irradiation. The radiations used were: 2537 A ultraviolet, 3500 to 4900 A long-ultraviolet and short visible, and 250 kvp1 x-rays. Both potassium retentivity and survival are decreased by these radiations. The dose-response of survival is about 16 times as sensitive as is potassium retentivity after 2537 A irradiation. Potassium retentivity is about twice as sensitive as survival after irradiation of 3500 to 4900 A. Survival after x-irradiation under aerobic conditions is five times as sensitive as potassium retentivity. Survival of cells irradiated with x-rays under anaerobic conditions was about half as sensitive as under aerobic conditions. The response of potassium retentivity to x-radiation at 25°C. under anaerobic conditions is only slightly affected below 160 kr, at which dose the slope abruptly increases to that obtained under aerobic conditions; lowering the temperature to 0°C. moves this point to about 300 kr. These differential effects are indicative of interaction of radiations with the yeast cell at sites that independently control survival and the retention of potassium.

scholarly journals The Tn3 beta-lactamase gene acts as a hotspot for meiotic recombination in yeast.

Genetics ◽  
1991 ◽  
Vol 127 (1) ◽  
pp. 39-51 ◽  
Author(s):  
A Stapleton ◽  
T D Petes
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Sequence ◽  
Dna Sequences ◽  
Meiotic Recombination ◽  
Genetic Distances ◽  
Crossing Over ◽  
Beta Lactamase ◽  
Yeast Saccharomyces Cerevisiae ◽  
Lactamase Gene ◽  
Bacterial Transposon

Abstract Although genetic distances are often assumed to be proportional to physical distances, chromosomal regions with unusually high (hotspots) or low (coldspots) levels of meiotic recombination have been described in a number of genetic systems. In general, the DNA sequences responsible for these effects have not been determined. We report that the 5' region of the beta-lactamase (ampR) gene of the bacterial transposon Tn3 is a hotspot for meiotic recombination when inserted into the chromosomes of the yeast Saccharomyces cerevisiae. When these sequences are homozygous, both crossing over and gene conversion are locally stimulated. The 5' end of the beta-lactamase gene is about 100-fold "hotter" for crossovers than an average yeast DNA sequence.

scholarly journals Negative heterosis for meiotic recombination rate in spermatocytes of the domestic chicken Gallus gallus

2021 ◽  
Vol 25 (6) ◽  
pp. 661-668
Author(s):  
L. P. Malinovskaya ◽  
K. V. Tishakova ◽  
T. I. Bikchurina ◽  
A. Yu. Slobodchikova ◽  
N. Yu. Torgunakov ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Meiotic Recombination ◽  
Recombination Rate ◽  
F1 Hybrids ◽  
Dna Breaks ◽  
Recombination Rates ◽  
Recombination Nodules ◽  
Double Strand Dna Breaks ◽  
Repair Protein ◽  
Benefits And Costs

Benefits and costs of meiotic recombination are a matter of discussion. Because recombination breaks allele combinations already tested by natural selection and generates new ones of unpredictable fitness, a high recombination rate is generally beneficial for the populations living in a fluctuating or a rapidly changing environment and costly in a stable environment. Besides genetic benefits and costs, there are cytological effects of recombination, both positive and negative. Recombination is necessary for chromosome synapsis and segregation. However, it involves a massive generation of double-strand DNA breaks, erroneous repair of which may lead to germ cell death or various mutations and chromosome rearrangements. Thus, the benefits of recombination (generation of new allele combinations) would prevail over its costs (occurrence of deleterious mutations) as long as the population remains sufficiently heterogeneous. Using immunolocalization of MLH1, a mismatch repair protein, at the synaptonemal complexes, we examined the number and distribution of recombination nodules in spermatocytes of two chicken breeds with high (Pervomai) and low (Russian Crested) recombination rates and their F1 hybrids and backcrosses. We detected negative heterosis for recombination rate in the F1 hybrids. Backcrosses to the Pervomai breed were rather homogenous and showed an intermediate recombination rate. The differences in overall recombination rate between the breeds, hybrids and backcrosses were mainly determined by the differences in the crossing over number in the seven largest macrochromosomes. The decrease in recombination rate in F1 is probably determined by difficulties in homology matching between the DNA sequences of genetically divergent breeds. The suppression of recombination in the hybrids may impede gene flow between parapatric populations and therefore accelerate their genetic divergence. 

scholarly journals Factors enforcing the species boundary between the human pathogens Cryptococcus neoformans and Cryptococcus deneoformans

2020 ◽  
Author(s):  
Shelby J. Priest ◽  
Marco A. Coelho ◽  
Verónica Mixão ◽  
Shelly Clancey ◽  
Yitong Xu ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Mismatch Repair ◽  
Dna Sequences ◽  
Meiotic Recombination ◽  
Genetic Recombination ◽  
Species Boundaries ◽  
Repair System ◽  
Hybrid Progeny ◽  
Dna Mismatch ◽  
Species Boundary

AbstractHybridization has resulted in the origin and variation in extant species, and hybrids continue to arise despite pre- and post-zygotic barriers that limit their formation and evolutionary success. One important system that maintains species boundaries in prokaryotes and eukaryotes is the mismatch repair pathway, which blocks recombination between divergent DNA sequences. Previous studies illuminated the role of the mismatch repair component Msh2 in blocking genetic recombination between divergent DNA during meiosis. Loss of Msh2 results in increased interspecific genetic recombination in bacterial and yeast models, and increased viability of progeny derived from yeast hybrid crosses. Hybrid isolates of two pathogenic fungal Cryptococcus species, Cryptococcus neoformans and Cryptococcus deneoformans, are isolated regularly from both clinical and environmental sources. In the present study, we sought to determine if loss of Msh2 would relax the species boundary between C. neoformans and C. deneoformans. We found that crosses between these two species in which both parents lack Msh2 produced hybrid progeny with increased viability and high levels of aneuploidy. Whole-genome sequencing revealed few instances of recombination among hybrid progeny and did not identify increased levels of recombination in progeny derived from parents lacking Msh2. Several hybrid progeny produced structures associated with sexual reproduction when incubated alone on nutrient-rich medium in light, a novel phenotype in Cryptococcus. These findings represent a unique, unexpected case where rendering the mismatch repair system defective did not result in increased meiotic recombination across a species boundary. This suggests that alternative pathways or other mismatch repair components limit meiotic recombination between homeologous DNA and enforce species boundaries in the basidiomycete Cryptococcus species.Author summarySeveral mechanisms enforce species boundaries by either preventing the formation of hybrids, known as pre-zygotic barriers, or preventing the viability and fecundity of hybrids, known as post-zygotic barriers. Despite these barriers, interspecific hybrids form at an appreciable frequency, such as hybrid isolates of the human fungal pathogenic species, Cryptococcus neoformans and Cryptococcus deneoformans, which are regularly isolated from both clinical and environmental sources. C. neoformans x C. deneoformans hybrids are typically highly aneuploid, sterile, and display phenotypes intermediate to those of either parent, although self-fertile isolates and transgressive phenotypes have been observed. One important mechanism known to enforce species boundaries or lead to incipient speciation is the DNA mismatch repair system, which blocks recombination between divergent DNA sequences during meiosis. The aim of this study was to determine if genetically deleting the DNA mismatch repair component Msh2 would relax the species boundary between C. neoformans and C. deneoformans. Progeny derived from C. neoformans x C. deneoformans crosses in which both parental strains lacked Msh2 had higher viability, and unlike previous studies in Saccharomyces, these Cryptococcus hybrid progeny had higher levels of aneuploidy and no observable increase in meiotic recombination at the whole-genome level.

Eds Of Radioactive Particles By Self-Induced Fluorescence

1990 ◽  
Vol 48 (2) ◽  
pp. 238-239
Author(s):  
Gregory L. Finch ◽  
Richard G. Cuddihy
Keyword(s):  
Electron Beam Irradiation ◽  
Nuclear Reactor ◽  
X Rays ◽  
Reactor Accident ◽  
Internal Radiation ◽  
X Ray ◽  
External Sources ◽  
X Irradiation ◽  
Available Information ◽  
Individual Particles

The elemental composition of individual particles is commonly measured by using energydispersive spectroscopic microanalysis (EDS) of samples excited with electron beam irradiation. Similarly, several investigators have characterized particles by using external monochromatic X-irradiation rather than electrons. However, there is little available information describing measurements of particulate characteristic X rays produced not from external sources of radiation, but rather from internal radiation contained within the particle itself. Here, we describe the low-energy (< 20 KeV) characteristic X-ray spectra produced by internal radiation self-excitation of two general types of particulate samples; individual radioactive particles produced during the Chernobyl nuclear reactor accident and radioactive fused aluminosilicate particles (FAP). In addition, we compare these spectra with those generated by conventional EDS.Approximately thirty radioactive particle samples from the Chernobyl accident were on a sample of wood that was near the reactor when the accident occurred. Individual particles still on the wood were microdissected from the bulk matrix after bulk autoradiography.

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