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1.
Analyses of evolution and maintenance of quantitative genetic variation depend on the mutation models assumed. Currently two polygenic mutation models have been used in theoretical analyses. One is the random walk mutation model and the other is the house-of-cards mutation model. Although in the short term the two models give similar results for the evolution of neutral genetic variation within and between populations, the predictions of the changes of the variation are qualitatively different in the long term. In this paper a more general mutation model, called the regression mutation model, is proposed to bridge the gap of the two models. The model regards the regression coefficient, γ, of the effect of an allele after mutation on the effect of the allele before mutation as a parameter. When γ = 1 or 0, the model becomes the random walk model or the house-of-cards model, respectively. The additive genetic variances within and between populations are formulated for this mutation model, and some insights are gained by looking at the changes of the genetic variances as γ changes. The effects of γ on the statistical test of selection for quantitative characters during macroevolution are also discussed. The results suggest that the random walk mutation model should not be interpreted as a null hypothesis of neutrality for testing against alternative hypotheses of selection during macroevolution because it can potentially allocate too much variation for the change of population means under neutrality.  相似文献   

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Abstract

A method for preparing ribosomes from Neurospora crassa is described in which che ribosomes prepared are free from the enzymes cytochrome c oxidase and NADPH-cytochrome c reductase, DNA and phospholipid material.  相似文献   

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Mitosis in Vegetative Nuclei of Neurospora Crassa   总被引:2,自引:0,他引:2       下载免费PDF全文
Somers CE  Wagner RP  Hsu TC 《Genetics》1960,45(6):801-810
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Genetic Control of Heterocaryosis in Neurospora Crassa   总被引:3,自引:0,他引:3       下载免费PDF全文
Holloway BW 《Genetics》1955,40(1):117-129
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A Series of Histidineless Mutants of Neurospora Crassa   总被引:6,自引:0,他引:6       下载免费PDF全文
Haas F  Mitchell MB  Ames BN  Mitchell HK 《Genetics》1952,37(3):217-226
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M. Bojko 《Genetics》1990,124(3):593-598
Heterozygotes for three long inversions on chromosome 1 were analyzed by serial reconstruction from electron micrographs. Measurements of loop lengths at different meiotic prophase substages revealed that the homologous synapsis of the inverted region was gradually replaced by nonhomologous synapsis as loops were eliminated during pachytene. This synaptic adjustment was apparently not affected by crossovers which occurred within the 150- and 160-cM long loops.  相似文献   

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In previous work, the asd-1 (ascus development) gene of the filamentous fungus Neurospora crassa was identified as a gene expressed preferentially during the sexual cycle and shown to be essential for normal sexual development. The asd-1 gene has been sequenced and further characterized. It contains two introns, the first of which is in-frame and inefficiently or differentially spliced. The predicted ASD-1 protein has extensive homology with rhamnogalacturonase B of Aspergillus aculeatus, which cleaves the backbone within the ramified hairy regions of pectin. In homozygous asd-1 crosses, sexual development is initiated and large numbers of normal-sized asci are formed. Ascospore delineation does not occur, however, and no sexual progeny are produced. As most asd-1 asci contain eight nuclei, the two meiotic divisions and subsequent mitotic division typical of normal crosses seem to occur, but the haploid nuclei are not partitioned into ascospores. In wild-type crosses, the ASD-1 protein is present in large amounts in croziers and young asci, but it is only faintly detectable in more mature asci containing developing ascospores. Models to explain the possible role of a rhamnogalacturonase in sexual development are presented.  相似文献   

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Fine Structure Analysis at the td Locus of Neurospora Crassa   总被引:2,自引:4,他引:2       下载免费PDF全文
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A Map of Linkage Group VI of Neurospora Crassa   总被引:4,自引:0,他引:4       下载免费PDF全文
Stadler DR 《Genetics》1956,41(4):528-543
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This report describes the purification from sonicates of Neurospora crassa conidia of a nuclease with extremely high specificity for single-stranded nucleic acids. The enzyme was purified 510-fold from streptomycin-treated sonicates in successive steps by (NH4)2SO4 fractionation, acetone fractionation, by chromatography on phosphocellulose, DEAE-cellulose, Sephadex G-200 and hydroxy apatite and, finally, by preparative polyacrylamide gel electrophoresis. The yield of purified enzyme was 7%. Only one protein component was detected by analytical polyacrylamide gel electrophoresis at pH8.9, but, in the presence of 1% sodium dodecyl sulfate and 1% mercaptoethanol at pH7.0, one minor component (approximately 10% of the total protein, mol. wt. approximately 77,000) and one major component (mol. wt. approximately 72,000) were detected. The enzyme degraded denatured DNA rapidly but did not release any acid-soluble material from native DNA. It also did not alter the sedimentation properties of native bacteriophage T7 DNA. The only action on native DNA that was detected was a slow conversion of the superhelical form of bacteriophage S13 DNA to the open circle form. The products of a 10% digest (10% acid-soluble material) of denatured DNA contained 5′-mono-nucleotides and oligonucleotides (di- to decanucleotides) in a ratio of 3 to 1, indicating that the digestion was predominantly exonucleolytic in character.  相似文献   

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