Interchange polymorphism in natural populations of Allium paniculatum L. (Liliaceae): nature, frequency, effects, and mechanism of maintenance

1986 ◽  
Vol 28 (3) ◽  
pp. 348-357 ◽  
Author(s):  
R. Lozano ◽  
C. Ruiz Rejón ◽  
M. Ruiz Rejón
Keyword(s):  
Chiasma Frequency ◽  
Vegetative Reproduction ◽  
Spontaneous Mutation ◽  
Natural Populations ◽  
Egg Cell ◽  
Satellite Chromosome ◽  
Spontaneous Mutation Rate ◽  
Selection Equilibrium ◽  
Nature Frequency ◽  
Reproductive Characters

A reciprocal translocation was found with a high frequency (average 44.44%) in four natural populations of Allium paniculatum L. (Liliaceae) from the South of Spain. The chromosomes involved are 1 and 7. The translocation is reciprocal and unequal. Chiasma frequency in the chromosomes not involved in the interchange is not affected, but chiasma frequency is decreased in the translocated chromosomes in the heterozygotes. As a satellite chromosome is involved in the interchange, the nucleolus is associated with the quadrivalent and the pattern of nucleolus formation is changed in heterozygotes, which have a lower mean number of nucleoli [Formula: see text] than homozygous standard individuals [Formula: see text]. The spontaneous mutation rate for interchanges during the early stages of microsporogenesis is high (μ = 1.08 × 10−2). No interchange homozygotes were found in any of the four populations analyzed. Furthermore, a comparative analysis of heterozygous (HT) and homozygous standard (HM) individuals in two populations demonstrated that homozygous standard plants show, on the whole, higher fitness than the heterozygotes. This can be attributed to a greater egg cell fertility and seed set. The possible causes of maintenance are discussed: the interchange in A. paniculatum is probably not maintained by overdominance for generative reproductive characters, nor by a mutation–selection equilibrium. One possibility, that heterozygotes have superior vegetative reproduction, still remains open for future investigation.Key words: Allium paniculatum, interchange polymorphism, fitness.

scholarly journals Spontaneous mutations and the origin and maintenance of quantitative genetic variation

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Wen Huang ◽  
Richard F Lyman ◽  
Rachel A Lyman ◽  
Mary Anna Carbone ◽  
Susan T Harbison ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Quantitative Traits ◽  
Spontaneous Mutation ◽  
Natural Populations ◽  
Empirical Work ◽  
Stabilizing Selection ◽  
Spontaneous Mutation Rate ◽  
Evolutionary Forces ◽  
Quantitative Genetic

Mutation and natural selection shape the genetic variation in natural populations. Here, we directly estimated the spontaneous mutation rate by sequencing new Drosophila mutation accumulation lines maintained with minimal natural selection. We inferred strong stabilizing natural selection on quantitative traits because genetic variation among wild-derived inbred lines was much lower than predicted from a neutral model and the mutational effects were much larger than allelic effects of standing polymorphisms. Stabilizing selection could act directly on the traits, or indirectly from pleiotropic effects on fitness. However, our data are not consistent with simple models of mutation-stabilizing selection balance; therefore, further empirical work is needed to assess the balance of evolutionary forces responsible for quantitative genetic variation.

scholarly journals Genetic barriers to gene flow separate divergent substitution rates across a butterfly hybrid zone

2021 ◽  
Author(s):  
Tianzhu Xiong ◽  
Xueyan Li ◽  
Masaya Yago ◽  
James Mallet
Keyword(s):  
Gene Flow ◽  
Molecular Evolution ◽  
Hybrid Zone ◽  
Substitution Rate ◽  
Spontaneous Mutation ◽  
Natural Populations ◽  
Gene Pools ◽  
Spontaneous Mutation Rate ◽  
Substitution Rates ◽  
Species Specific

Substitution rate defines the fundamental timescale of molecular evolution which often varies in a species-specific manner. However, it is unknown under what conditions lineage-specific rates can be preserved between natural populations with frequent hybridization. Here, we show in a hybrid zone between two butterflies, Papilio syfanius and Papilio maackii, that genome-wide barriers to gene flow can effectively separate different rates of molecular evolution in linked regions. The increased substitution rate in the lowland lineage can be largely explained by temperature-induced changes to the spontaneous mutation rate. A novel method based on entropy is developed to test for the existence of barrier loci using a minimal number of samples from the hybrid zone, a robust framework when system complexity far exceeds sample information. Overall, our results suggest that during the process of speciation, the separation of substitution rates can occur locally in the genome in parallel to the separation of gene pools.

scholarly journals POPULATION GENETICS OF ALLOZYME VARIATION IN NEUROSPORA INTERMEDIA

Genetics ◽  
1975 ◽  
Vol 80 (4) ◽  
pp. 785-805
Author(s):  
P T Spieth
Keyword(s):  
Genetic Variation ◽  
Vegetative Reproduction ◽  
Vascular Plant ◽  
Natural Populations ◽  
Allozyme Variation ◽  
Regular Feature ◽  
Local Populations ◽  
Neurospora Intermedia ◽  
Pattern Of Variation ◽  
High Level

ABSTRACT Electrophoretically detectable variation in the fungus Neurospora intermedia has been surveyed among isolates from natural populations in Malaya, Papua, Australia and Florida. The principal result is a pattern of genetic variation within and between populations that is qualitatively no different than the well documented patterns for Drosophila and humans. In particular, there is a high level of genetic variation, the majority of which occurs at the level of local populations. Evidence is presented which argues that N. intermedia has a population structure analogous to that of an annual vascular plant with a high level of vegetative reproduction. Sexual reproduction appears to be a regular feature in the biology of the species. Substantial heterokaryon function seems unlikely in natural populations of N. intermedia. Theoretical considerations concerning the mechanisms underlying the observed pattern of variation most likely should be consistent with haploid selection theory. The implications of this constraint upon the theory are discussed in detail, leading to the presentation of a model based upon the concept of environmental heterogeneity. The essence of the model, which is equally applicable to haploid and diploid situations, is a shifting distribution of multiple adaptive niches among local populations such that a given population has a small net selective pressure in favor of one allele or another, depending upon its particular distribution of niches. Gene flow among neighboring populations with differing net selective pressures is postulated as the principal factor underlying intrapopulational allozyme variation.

A Mutation in a Saccharomyces cerevisiae Gene (RAD3) Required for Nucleotide Excision Repair and Transcription Increases the Efficiency of Mismatch Correction

Genetics ◽  
1996 ◽  
Vol 144 (2) ◽  
pp. 459-466 ◽  
Author(s):  
Yingying Yang ◽  
Anthony L Johnson ◽  
Leland H Johnston ◽  
Wolfram Siede ◽  
Errol C Friedberg ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mismatch Repair ◽  
Excision Repair ◽  
Spontaneous Mutation ◽  
Surprising Result ◽  
Spontaneous Mutation Rate ◽  
Mismatch Correction ◽  
Nucleotide Excision ◽  
Repair Genes ◽  
Type Strains

Abstract RAD3 functions in DNA repair and transcription in Saccharomyces cerevisiae and particular rad3 alleles confer a mutator phenotype, possibly as a consequence of defective mismatch correction. We assessed the potential involvement of the Rad3 protein in mismatch correction by comparing heteroduplex repair in isogenic rad3-1 and wild-type strains. The rad3-1 allele increased the spontaneous mutation rate but did not prevent heteroduplex repair or bias its directionality. Instead, the efficiency of mismatch correction was enhanced in the rad3-1 strain. This surprising result prompted us to examine expression of yeast mismatch repair genes. We determined that MSH2, but not MLH1, is transcriptionally regulated during the cell-cycle like PMSl, and that rad3-1 does not increase the transcript levels for these genes in log phase cells. These observations suggest that the rad3-1 mutation gives rise to an enhanced efficiency of mismatch correction via a process that does not involve transcriptional regulation of mismatch repair. Interestingly, mismatch repair also was more efficient when error-editing by yeast DNA polymerase δ was eliminated. We discuss our results in relation to possible mechanisms that may link the rad3-1 mutation to mismatch correction efficiency.

scholarly journals Nature of Deleterious Mutation Load in Drosophila

Genetics ◽  
1996 ◽  
Vol 144 (4) ◽  
pp. 1993-1999 ◽  
Author(s):  
Peter D Keightley
Keyword(s):  
Deleterious Mutation ◽  
Spontaneous Mutation ◽  
Mutation Accumulation ◽  
Mutation Rates ◽  
Mutation Load ◽  
Spontaneous Mutation Rate ◽  
A Minor ◽  
Chromosome I ◽  
Balancer Chromosomes ◽  
Balancer Chromosome

Much population genetics and evolution theory depends on knowledge of genomic mutation rates and distributions of mutation effects for fitness, but most information comes from a few mutation accumulation experiments in Drosophila in which replicated chromosomes are sheltered from natural selection by a balancer chromosome. I show here that data from these experiments imply the existence of a large class of minor viability mutations with approximately equivalent effects. However, analysis of the distribution of viabilities of chromosomes exposed to EMS mutagenesis reveals a qualitatively different distribution of effects lacking such a minor effects class. A possible explanation for this difference is that transposable element insertions, a common class of spontaneous mutation event in Drosophila, frequently generate minor viability effects. This explanation would imply that current estimates of deleterious mutation rates are not generally applicable in evolutionary models, as transposition rates vary widely. Alternatively, much of the apparent decline in viability under spontaneous mutation accumulation could have been nonmutational, perhaps due to selective improvement of balancer chromosomes. This explanation accords well with the data and implies a spontaneous mutation rate for viability two orders of magnitude lower than previously assumed, with most mutation load attributable to major effects.

Gonad Temperature and Spontaneous Mutation-rate in Man

Nature ◽  
1957 ◽  
Vol 180 (4599) ◽  
pp. 1433-1434 ◽  
Author(s):  
LARS EHEENBERG ◽  
GÜNTER VON EHRENSTEIN ◽  
ARNE HEDGRAN
Keyword(s):  
Mutation Rate ◽  
Spontaneous Mutation ◽  
Spontaneous Mutation Rate

Scope of action of the immunoglobulin mutator system

Genome ◽  
1989 ◽  
Vol 31 (1) ◽  
pp. 118-121 ◽  
Author(s):  
Matthias R. Wabl ◽  
Hans-Martin Jäck ◽  
R. C. von Borstel ◽  
Charles M. Steinberg
Keyword(s):  
B Cell ◽  
Mutation Rate ◽  
Heavy Chain ◽  
B Lymphocyte ◽  
Somatic Hypermutation ◽  
Spontaneous Mutation ◽  
Cell Lineage ◽  
Variable Region ◽  
High Rate ◽  
Spontaneous Mutation Rate

The authors have developed a method to measure the rate of spontaneous mutations taking place in IgH, the gene encoding the immunoglobulin heavy chain. When an amber chain-termination codon mutates to a sense codon, translation of the polypeptide chain will be completed, and mutant cells producing the heavy chain can be detected with a fluorescent labelled antibody. The protocol used is the compartmentalization test which minimizes any effect of selection. In subclones of the pre-B lymphocyte line 18–81, the spontaneous mutation rate in the part of IgH encoding the variable region is somewhat greater than 10−5 mutations per base pair per generation. This supports the hypothesis that hypermutation is not dependent on cell stimulation by an antigen. In a hybrid between a cell of this line and a myeloma (which represents the terminal stage of the B-cell lineage), the mutation rate was too low to be determined by this test, less than 10−9. When the same loss to gain procedure system was used with an opal chain-terminating codon in the part of IgH encoding the constant region (Cμ), a high rate of reversion by deletion was found. Long (more than one exon) and short (less than one exon) deletions occurred at rates of 1.7 × 10−5 and 1.4 × 10−7 per generation, respectively. It is thought that the high rate of deletion is not related to somatic hypermutation but rather to DNA rearrangement during the heavy-chain class switch, which is occurring in these pre-B cell lines. The point mutation rate was too low to be detected above the background of deletion mutants, less than 5 × 10−8. The immunoglobulin mutator system works weakly, if at all, on two other, nonimmunoglobulin, genes tested: B2m (β2 microglobulin) and the gene for ouabain resistance.Key words: pre-B lymphocyte, B lymphocyte, spontaneous mutation rate, compartmentalization test, deletion mutation, hypermutation.

scholarly journals Mutation avoidance and DNA repair proficiency in Ustilago maydis are differentially lost with progressive truncation of the REC1 gene product.

1995 ◽  
Vol 15 (10) ◽  
pp. 5329-5338 ◽  
Author(s):  
K Onel ◽  
M P Thelen ◽  
D O Ferguson ◽  
R L Bennett ◽  
W K Holloman
Keyword(s):  
Amino Acid ◽  
Mutation Rate ◽  
Spontaneous Mutation ◽  
Ustilago Maydis ◽  
Radiation Sensitivity ◽  
Open Reading Frame ◽  
Exonuclease Activity ◽  
Amino Acid Residues ◽  
Spontaneous Mutation Rate ◽  
Reading Frame

The REC1 gene of Ustilago maydis has an uninterrupted open reading frame, predicted from the genomic sequence to encode a protein of 522 amino acid residues. Nevertheless, an intron is present, and functional activity of the gene in mitotic cells requires an RNA processing event to remove the intron. This results in a change in reading frame and production of a protein of 463 amino acid residues. The 3'-->5' exonuclease activity of proteins derived from the REC1 genomic open reading frame, the intronless open reading frame, and several mutants was investigated. The mutants included a series of deletions constructed by removing restriction fragments at the 3' end of the cloned REC1 gene and a set of mutant alleles previously isolated in screens for radiation sensitivity. All of these proteins were overproduced in Escherichia coli as N-terminal polyhistidine-tagged fusions that were subsequently purified by immobilized metal affinity chromatography and assayed for 3'-->5' exonuclease activity. The results indicated that elimination of the C-terminal third of the protein did not result in a serious reduction in 3'-->5' exonuclease activity, but deletion into the midsection caused a severe loss of activity. The biological activity of the rec1-1 allele, which encodes a truncated polypeptide with full 3'-->5' exonuclease activity, and the rec1-5 allele, which encodes a more severely truncated polypeptide with no exonuclease activity, was investigated. The two mutants were equally sensitive to the lethal effect of UV light, but the spontaneous mutation rate was elevated 10-fold over the wild-type rate in the rec1-1 mutant and 100-fold in the rec1-5 mutant. The elevated spontaneous mutation rate correlated with the ablation of exonuclease activity, but the radiation sensitivity did not. These results indicate that the C-terminal portion of the Rec1 protein is not essential for exonuclease activity but is crucial in the role of REC1 in DNA damage repair.

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