scholarly journals New rust resistance specificities associated with recombination in the Rp1 complex in maize.

Genetics ◽  
1995 ◽  
Vol 141 (1) ◽  
pp. 373-381 ◽  
Author(s):  
T E Richter ◽  
T J Pryor ◽  
J L Bennetzen ◽  
S H Hulbert
Keyword(s):  
Gene Conversion ◽  
Resistance Genes ◽  
Partial Resistance ◽  
Rust Resistance ◽  
Crossing Over ◽  
Unequal Crossing Over ◽  
Genetic Reassortment ◽  
Marker Exchange

Abstract We address the question of whether genetic reassortment events, including unequal crossing over and gene conversion, at the Rp1 complex are capable of generating novel resistance specificities that were not present in the parents. Some 176 events involving genetic reassortment within the Rp1 complex were screened for novel resistance specificities with a set of 11 different rust biotypes. Most (150/176) of the events were susceptible to all tested rust biotypes, providing no evidence for new specificities. Eleven events selected as double-resistant recombinants, when screened with the 11 test biotypes, showed the combined resistance of the two parental types consistent with a simple recombination and pyramiding of the parental resistances. Nine events selected either as having partial resistance or complete susceptibility to a single biotype possessed resistance to a subset of the biotypes that the parents were resistant to, suggesting segregation of resistance genes present in the parental Rp1 complex. Four events gave rise to novel specificities being resistant to at least one rust biotype to which both parents were susceptible. All four had flanking marker exchange, demonstrating that crossing over within the Rp1 complex is associated with the appearance of new rust resistance specificities.

scholarly journals Recombination and Spontaneous Mutation at the Major Cluster of Resistance Genes in Lettuce (Lactuca sativa)

Genetics ◽  
2001 ◽  
Vol 157 (2) ◽  
pp. 831-849
Author(s):  
Doris B Chin ◽  
Rosa Arroyo-Garcia ◽  
Oswaldo E Ochoa ◽  
Rick V Kesseli ◽  
Dean O Lavelle ◽  
...  
Keyword(s):  
Gene Conversion ◽  
Resistance Genes ◽  
Spontaneous Mutation ◽  
Large Chromosome ◽  
Crossing Over ◽  
Unequal Crossing Over ◽  
Chimeric Genes ◽  
Recessive Mutations ◽  
Major Cluster ◽  
Genetic Mechanisms

Abstract Two sets of overlapping experiments were conducted to examine recombination and spontaneous mutation events within clusters of resistance genes in lettuce. Multiple generations were screened for recombinants using PCR-based markers flanking Dm3. The Dm3 region is not highly recombinagenic, exhibiting a recombination frequency 18-fold lower than the genome average. Recombinants were identified only rarely within the cluster of Dm3 homologs and no crossovers within genes were detected. Three populations were screened for spontaneous mutations in downy mildew resistance. Sixteen Dm mutants were identified corresponding to spontaneous mutation rates of 10–3 to 10–4 per generation for Dm1, Dm3, and Dm7. All mutants carried single locus, recessive mutations at the corresponding Dm locus. Eleven of the 12 Dm3 mutations were associated with large chromosome deletions. When recombination could be analyzed, deletion events were associated with exchange of flanking markers, consistent with unequal crossing over; however, although the number of Dm3 paralogs was changed, no novel chimeric genes were detected. One mutant was the result of a gene conversion event between Dm3 and a closely related homolog, generating a novel chimeric gene. In two families, spontaneous deletions were correlated with elevated levels of recombination. Therefore, the short-term evolution of the major cluster of resistance genes in lettuce involves several genetic mechanisms including unequal crossing over and gene conversion.

Evidence for the involvement of gene conversion in meiotic instability of the Rp1 rust resistance genes of maize

Genome ◽  
1994 ◽  
Vol 37 (5) ◽  
pp. 742-746 ◽  
Author(s):  
Gongshe Hu ◽  
Scot Hulbert
Keyword(s):  
Gene Conversion ◽  
Rust Resistance ◽  
Fragment Length Polymorphism ◽  
Crossing Over ◽  
Resistance Locus ◽  
Unequal Crossing Over ◽  
Rust Resistance Genes ◽  
Family Restriction ◽  
Restriction Fragment Length ◽  
Recombination Gene

Rp1 is a complex rust resistance locus of maize. Susceptible recombinants can be observed at variable frequencies from different Rp1 heterozygotes and homozygotes by crossing-over and unequal crossing-over. In addition, susceptible progeny have been observed from one heterozygote that were not associated with crossing-over, as indicated by flanking marker analysis. We analyzed testcross progeny from this cross (Rp1-C/Rp1-J) and a related cross (Rp1-F/Rp1-J) to identify noncrossover type derivatives, to estimate their frequency, and to determine the mechanism by which they arise. Testcross progeny were screened sequentially with two different rust isolates to assay each gene individually. Both susceptible noncrossover types and those with the combined resistance of each parent were identified in approximately equal frequencies. Patterns of recombination indicated that the noncrossover type derivatives arose by gene conversion as opposed to mutation or intrachromosomal crossing-over. While gene conversion events were observed frequently in both crosses (approx. 7 × 10−4), they were less frequent than crossover derivatives. Key words: Puccinia, disease resistance, recombination, gene family, restriction fragment length polymorphism.

Unequal crossing-over and gene conversion at the amplifiedCUP1 locus of yeast

1990 ◽  
Vol 222 (2-3) ◽  
pp. 304-310 ◽  
Author(s):  
Juliet W. Welch ◽  
Daniel H. Maloney ◽  
Seymour Fogel
Keyword(s):  
Gene Conversion ◽  
Crossing Over ◽  
Unequal Crossing Over

Biased gene conversion is not occurring among rDNA repeats in the Brassica triangle

Genome ◽  
1996 ◽  
Vol 39 (1) ◽  
pp. 150-154 ◽  
Author(s):  
Elizabeth R. Waters ◽  
Barbara A. Schaal
Keyword(s):  
Genetic Variation ◽  
Key Words ◽  
Gene Conversion ◽  
Relative Frequency ◽  
Brassica Species ◽  
Multigene Families ◽  
Crossing Over ◽  
Common Phenomenon ◽  
Unequal Crossing Over ◽  
Biased Gene Conversion

Hybridization is a common phenomenon that results in complex genomes. How ancestral genomes interact in hybrids has long been of great interest. Recombination among ancestral genomes may increase or decrease genetic variation. This study examines rDNA from members of the Brassica triangle for evidence of gene conversion across ancestral genomes. Gene conversion is a powerful force in the evolution of multigene families. It has previously been shown that biased gene conversion can act to homogenize rDNA repeats within hybrid genomes. Here, we find no evidence for biased gene conversion or unequal crossing over across ancestral genomes in allotetraploid Brassica species. We suggest that, while basic genomic processes are shared by all organisms, the relative frequency of these processes and their evolutionary importance may differ among lineages. Key words : Brassica, rDNA, gene conversion, allotetraploids.

Structural variation and dynamics of the nuclear ribosomal intergenic spacer region in key members of the Gibberella fujikuroi species complex

Genome ◽  
2013 ◽  
Vol 56 (4) ◽  
pp. 205-213 ◽  
Author(s):  
Salvador Mirete ◽  
Belén Patiño ◽  
Miguel Jurado ◽  
Covadonga Vázquez ◽  
María Teresa González-Jaén
Keyword(s):  
Gene Conversion ◽  
Species Complex ◽  
Intergenic Spacer ◽  
Gibberella Fujikuroi ◽  
Crossing Over ◽  
Repeat Elements ◽  
Unequal Crossing Over ◽  
Intergenic Spacer Region ◽  
Species Specific ◽  
Gibberella Fujikuroi Species Complex

The intergenic spacer (IGS) region of the ribosomal DNA was cloned and sequenced in eight species within the Gibberella fujikuroi species complex with anamorphs in the genus Fusarium, a group that includes the most relevant toxigenic species. DNA sequence analyses revealed two categories of repeated elements: long repeats and short repeats of 125 and 8 bp, respectively. Long repeats were present in two copies and were conserved in all the species analyzed, whereas different numbers of short repeat elements were observed, leading to species-specific IGS sequences with different length. In Fusarium subglutinans and Fusarium nygamai, these differences seemed to be the result of duplication and deletion events. Here, we propose a model based on unequal crossing over that can explain these processes. The partial IGS sequence of 22 Fusarium proliferatum isolates was also obtained to study variation at the intraspecific level. The results revealed no differences in terms of number or pattern of repeated elements and detected frequent gene conversion events. These results suggest that the homogenization observed at the intraspecific level might not be achieved primarily by unequal crossing-over events but rather by processes associated with recombination such as gene conversion events.

scholarly journals Simulation study of a multigene family, with special reference to the evolution of compensatory advantageous mutations.

Genetics ◽  
1992 ◽  
Vol 132 (1) ◽  
pp. 247-252 ◽  
Author(s):  
C J Basten ◽  
T Ohta
Keyword(s):  
Model Selection ◽  
Gene Conversion ◽  
Simulation Study ◽  
Multigene Family ◽  
Negative Selection ◽  
Crossing Over ◽  
Simulation Studies ◽  
Unequal Crossing Over ◽  
Deleterious Alleles ◽  
Compensatory Mutations

Abstract We investigate the evolution of a multigene family incorporating the forces of drift, mutation, gene conversion, unequal crossing over and selection. The use of simulation studies is required due to the complexity of the model. Selection is modeled in two modes: positive selection as a function of the number of different beneficial alleles and negative selection against deleterious alleles. We assume that gene conversion is unbiased, and that all mutations are initially deleterious. Compensation between mutants creates beneficial and neutral alleles, and allowances are made for compensatory mutations either within or between the members of a multigene family. We find that gene conversion can enhance the rate of acquisition of compensatory advantageous mutations when genes are redundant.

Mapping Unequal Crossing over Hotspot Region of Simple Sequence Repeat in Maize

2009 ◽  
Vol 35 (5) ◽  
pp. 958-961
Author(s):  
Ji-Hua TANG ◽  
Xi-Qing MA ◽  
Wen-Tao TENG ◽  
Jian-Bing YAN ◽  
Jing-Rui DAI ◽  
...  
Keyword(s):  
Simple Sequence Repeat ◽  
Crossing Over ◽  
Sequence Repeat ◽  
Unequal Crossing Over ◽  
Simple Sequence

Characterization of Wheat Stripe Rust Resistance Genes in Shaanmai 139

2010 ◽  
Vol 36 (1) ◽  
pp. 109-114 ◽  
Author(s):  
Hong ZHANG ◽  
Zhi-Long REN ◽  
Yin-Gang HU ◽  
Chang-You WANG ◽  
Wan-Quan JI
Keyword(s):  
Stripe Rust ◽  
Resistance Genes ◽  
Rust Resistance ◽  
Stripe Rust Resistance ◽  
Wheat Stripe Rust ◽  
Rust Resistance Genes

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

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