Aberrant segregation of R-locus genes in male progeny from incompatible crosses in Mormoniella

Crosses of females from Mormoniella stocks containing pe-333 type cross incompatibility with males from stocks lacking the incompatibility produced progeny that included 29 males with unexpected eye colors. Eight of these males gave rise to stocks that included some individuals with "speckled" eyes, containing sectors or spots of different colors. In these stocks there were unexpectedly low frequencies of transmission of the new phenotypes to progeny. Phenotypes, and results of crosses, are consistent with the hypothesis that the original males and the stocks that they sired contained extra bits of chromatin contributed by the sperm of the males used in the incompatible crosses. In these stocks, these pieces are transmitted with greater frequency by sperm than by eggs, and are occasionally lost in mitosis (producing "speckled" eyes). Data also indicate that the extra chromatin contains only the O and S factors, or the O factor alone, of the eye color locus R. Examination of spermatogonia shows an extra piece of chromatin in cells of males with phenotypes that suggest the presence of such a piece. The piece has not been found in spermatogonia of controls.     

Pollen tube behavior in yellow passion fruit following compatible and incompatible crosses

Pistil squashes were used to examine the growth of Passiflora edulis f. flavicarpa Deg pollen tubes in self-compatible and self-incompatible crosses. Compatible tubes typically showed a uniform layer of callose deposition in the walls and in small plugs spaced at regular intervals within the tube. Two sites of rejection were observed in incompatible crosses: the stigma and on some occasions the style, especially in anomalous crosses. In the style the inhibition of pollen-tube growth occurred in both the upper and middle parts of the transmitting tract. These findings are consistent with the hypothesis that suggests the presence of a gametophytic gene which acts in association with the sporophytic S-gene in P. edulis. Received: 12 October 1998 / Accepted: 2 December 1999     

Wolbachia infection influences the development of Culex pipiens embryo in incompatible crosses

Wolbachia are maternally inherited endosymbiotic bacteria that infect many arthropod species and have evolved several different ways for manipulating their host, the most frequent being cytoplasmic incompatibility (CI). CI leads to embryo death in crosses between infected males and uninfected females, as well as in crosses between individuals infected by incompatible Wolbachia strains. In the mosquito Culex pipiens, previous studies suggested developmental variation in embryos stemming from different incompatible crosses. We have investigated this variation in different incompatible crosses. Unhatched eggs were separated into three classes based upon the developmental stage reached by the embryos. We found that incompatible crosses involving uninfected females produced only embryos whose development was arrested at a very early stage, irrespective of the Wolbachia variant infecting the male. These results differ from other host species where a developmental gradient that could reach late stages of embryogenesis or even living larvae was observed, and indicate a novel peculiarity of CI mechanism in C. pipiens. By contrast, all incompatible crosses with infected C. pipiens females produced embryos of all three classes. The proportion of embryo classes appeared to be associated with the strains involved, suggesting specific CI properties in different incompatible crosses. In addition, the contribution of parental genome was characterized in embryo classes using molecular markers for each chromosome. Embryo phenotypes appeared linked to the paternal chromosomes' contribution, as described in Drosophila simulans. However, this contribution varied according to maternal infection and independently of male factors.     

Stable and unstable mutations in aberrant ratio stocks of maize

Aberrant Ratio (AR) stocks of maize were tested for transposition activity. Lines exhibiting AR and homozygous for the dominant alleles at the Sh Bz and Wx loci in the short arm of chromosome 9 were crossed as males to a sh bz wx tester. Among a population of 346,201 kernels, eight mutations of sh and two of bz were recovered. Eight of the ten mutations survived and none was as vigorous as its normal sibs. At least five of the sh mutants appear to be unstable in F₂ and subsequent generations. An unexpected observation was the high incidence of somatic loss of chromosome 9 markers (Sh Bz and Wx), indicating chromosome breakage or nondisjunction. Southern blot hybridization analysis of the sh alterations indicate that all but one mutant are associated with structural DNA rearrangements at the shrunken locus. Possible mechanisms by which these alterations arose are discussed.     

Doubled haploids of novel trigenomic Brassica derived from various interspecific crosses

To develop doubled haploid (DH) mapping populations of hexaploid Brassica, 10 F₁ hybrids derived from crosses between allohexaploid Brassica parents were evaluated in this study. The allohexaploid Brassica parents were selfed progenies of unique interspecific crosses between Brassica rapa (genome AA) × B. carinata (BBCC), B. nigra (BB) × B. napus (AACC), and a complex cross between B. juncea (AABB), B. napus and B. carinata, with relatively stable chromosome number (2n = 54). Hexaploid status and chromosome behavior during meiosis I in four promising F₁ hybrids were assessed using microscopy and flow cytometry, and progeny were obtained following microspore culture. Hybrids H11-2 and H16-1 demonstrated higher amenability for embryo generation, plantlet regeneration, and frequency of production of DH microspore-derived progeny of hexaploid DNA content (6x) compared to hybrids H08-1 and H24-1. A total of 370 6x DH progeny were selected out of 693 plantlets from H11-2, 241/436 from H16-1, 23/54 from H08-1, and 21/56 from H24-1. DH progenies of hybrids H11-2 and H16-1 were then designated as promising mapping populations of a new hexaploid Brassica species.     

QTL mapping under truncation selection in homozygous lines derived from biparental crosses

In plant breeding, a large number of progenies that will be discarded later in the breeding process must be phenotyped and marker genotyped for conducting QTL analysis. In many cases, phenotypic preselection of lines could be useful. However, in QTL analyses even moderate preselection can have a significant effect on the power of QTL detection and estimation of effects of the target traits. In this study, we provide exact formulas for quantifying the change of allele frequencies within marker classes, expectations of marker contrasts and the variance of the marker contrasts under truncation selection, for the general case of two QTL affecting the target trait and a correlated trait. We focused on homozygous lines derived at random from biparental crosses. The effects of linkage between the marker and the QTL under selection as well as the effect of selection on a correlated trait can be quantified with the given formulas. Theoretical results clearly show that depending on the magnitude of QTL effects, high selection intensities can lead to a dramatic reduction in power of QTL detection and that approximations based on the infinitesimal model deviate substantially from exact solutions. The presented formulas are valuable for choosing appropriate selection intensity when performing QTL mapping experiments on the data on phenotypically preselected traits and enable the calculation and bias correction of the effects of QTL under selection. Application of our theory to experimental data revealed that selection-induced bias of QTL effects can be successfully corrected.     

The effect of pollen irradiation on segregation in spring barley crosses

Observations on the Ml, M2 and M3 generations from three barley crosses confirmed that pollen irradiation can cause deviations from expected segregation ratios for certain characters. The reduced fertility observed in the Ml and M2 generations of these crosses could be problematical in breeding programmes. It was of particular interest that at the highest dose rate used for the cross TS117 × Scots Bere there was no expression of the 6-row character, which is controlled by a recessive paternal factor.     

Genome-wide dissection of segregation distortion using multiple inter-subspecific crosses in rice

Mendelian inheritance can ensure equal segregation of alleles from parents to offspring, which provides fundamental basis for genetics and molecular biology. Segregation distortion(SD) leads to preferential transmission of certain alleles from generation to generation. Such violation of Mendelian genetic principle is often accompanied by reproductive isolation and eventually speciation. Although SD is observed in a wide range of species from plants to animals, genome-wide dissection of such biased transmission of gametes is rare. Using nine inter-subspecific rice crosses, a genome-wide screen for SD loci is performed, which reveals 61 single-locus quantitative trait loci and 194 digenic interactions showing distorted transmission ratio, among which 24 new SD loci are identified. Biased transmission of alleles is observed in all nine crosses, suggesting that SD exists extensively in rice populations. 72.13% distorted regions are repeatedly detected in multiple populations, and the most prevalent SD hotspot that observed in eight populations is mapped to chromosome 3. Xian alleles are transmitted at higher frequencies than geng alleles in inter-subspecific crosses, which change the genetic composition of the rice populations. Epistatic interaction contributes significantly to the deviation of Mendelian segregation at the whole-genome level in rice, which is distinct from that in animals. These results provide an extensive archive for investigating the genetic basis of SD in rice, which have significant implications in understanding the reproductive isolation and formation of inter-subspecific barriers during the evolution.     

Upf1 stimulates degradation of the product derived from aberrant messenger RNA containing a specific nonsense mutation by the proteasome

Aberrant messenger RNAs containing a premature termination codon (PTC) are eliminated by the nonsense‐mediated mRNA decay (NMD) pathway. Here, we show that a crucial NMD factor, up frameshift 1 protein (Upf1), is required for rapid proteasome‐mediated degradation of an aberrant protein (PTC product) derived from a PTC‐containing mRNA. Western blot and pulse–chase analyses revealed that Upf1 stimulates the degradation of specific PTC products by the proteasome. Moreover, the Upf1‐dependent, proteasome‐mediated degradation of the PTC product was also stimulated by mRNAs harbouring a faux 3′ untranslated region (3′‐UTR). These results indicate that protein stability might be regulated by an aberrant mRNA 3′‐UTR.     

Male and female roles in crosses of Aspergillus nidulans as revealed by vegetatively incompatible parents

To resolve the role of male and female nuclei and mitochondria in cleistothecium formation in the model organism Aspergillus nidulans, we analysed the genetic constituents of cleistothecia from crosses between vegetatively compatible and incompatible parents. We used markers that enabled us to determine the nuclear genotype of the cleistothecial wall and the nuclear and mitochondrial genotype of the ascospores. In compatible parents, nuclear genomes and cytoplasm usually mix in the vegetative hyphae prior to the formation of the sexual stage after which any cleistothecial composition is possible. In incompatible parents, the maternal strain contributes the nuclei for the cleistothecial wall and one nucleus as well as mitochondria for the ascospore origin. The paternal strain donates one nucleus for the ascospore origin. Only in crosses between vegetatively incompatible partners, it is possible to assign a female and male role to the parental strains. Our results confirm that the vegetative heterokaryotic stage is not a prerequisite for cleistothecium formation. Using this tool, we analysed sexual sporulation mutants for male or female sterility.     

Non-reciprocal recombination as an explanation of aberrant segregation in Chlamydomonas reinhardi

Summary In crosses of a p-aminobencoic acid requiring mutant of Chlamydomonas reinhard with the wildtype we observed besides the expected 4:4 segregation a surprisingly high frequency of aberrant segregation, all of which preferentially led to the wildtype. The only possible explanation of this finding is a non-reciprocal recombination, as mutations, trisomy and the loss of a tetrad cell with following additional division of a sister cell can be excluded. The molecular mechanism of non-reciprocal recombinations is still unknown. Nevertheless our findings are best understood, if we accept the hybrid-DNA model of Holliday, especially because this model is not only able to explain the 5:3 and 6:2 tetrads, but also the 7:1 and 8:0 segregations which occur at a much lower rate.The frequency of non-reciprocal recombinations could be reduced by irradiating zygotes at the very beginning of the germination period. If the X-rays were applicated 61/2 hours after induction of the germination, no clear aberrant segregation could be found.The reduction of the frequency of non-reciprocal recombinations by X-rays leads to the conclusion, that the mechanism of mutation and conversion are not identical. On the other hand we known many mutagenic substances which also cause non-reciprocal recombination. Thus it can be supposed that both the mechanisms have some steps in common.     

Variance of the parental genome contribution to inbred lines derived from biparental crosses

The expectation of the parental genome contribution to inbred lines derived from biparental crosses or backcrosses is well known, but no theoretical results exist for its variance. Our objective was to derive the variance of the parental genome contribution to inbred lines developed by the single-seed descent or double haploid method from biparental crosses or backcrosses. We derived formulas and tabulated results for the variance of the parental genome contribution depending on the chromosome lengths and the mating scheme used for inbred line development. A normal approximation of the probability distribution function of the parental genome contribution fitted well the exact distribution obtained from computer simulations. We determined upper and lower quantiles of the parental genome contribution for model genomes of sugar beet, maize, and wheat using normal approximations. These can be employed to detect essentially derived varieties in the context of plant variety protection. Furthermore, we outlined the application of our results to predict the response to selection. Our results on the variance of the parental genome contribution can assist breeders and geneticists in the design of experiments or breeding programs by assessing the variation around the mean parental genome contribution for alternative crossing schemes.     

Statistical tests for QTL and QTL-by-environment effects in segregating populations derived from line crosses

Quantitative trait locus (QTL) studies in plants frequently employ phenotypic data on a population of lines (doubled haploid lines, recombinant inbred lines, etc.) tested in multiple environments. An important feature of such data is the genetic correlation among observations on the same genotype in different environments. Detection of QTL-by-environment interaction requires tests which take this correlation into account. In this article, a comparison was made of the properties of several such tests by means of simulation. The results indicate that a split-plot analysis of variance (anova), being an approximate method, tends to be too liberal under departures from the Huynh-Feldt condition. A standard two-way anova, which ignores genetic correlation, yields inappropriate tests and should be avoided. In contrast, mixed model approaches as well as univariate and multivariate repeated-measures anova yield valid results. This supports the use of a flexible mixed model framework in more complex settings, which are difficult to tackle by repeated-measures anova.This paper is dedicated to Prof. Dr. H. F. Utz on the occasion of his 65th birthday.     

Paternity and ploidy segregation of progenies derived from tetraploid Malus xiaojinensis

Apomixis is usually subdivided into parthenogenesis, apogamy, and apospory on the basis of different mechanisms of development and cytogenetic effects. Although most plants and animals undergo sexual reproduction to multiply, it is important to understand the role of apomixis in plant reproduction because of its useful applications in the breeding and propagation of some crops. Tetraploid Malus xiaojinensis Cheng et Jiang is a typical facultative apomictic plant species. Paternity and ploidy analyses of M. xiaojinensis seedlings were performed with flow cytometry in conjunction with microsatellite and single nucleotide polymorphism markers. The proportion of apomictic derived progeny of M. xiaojinensis × Malus baccata was 54.05, 53.96, and 43.55 % from 2008 to 2010, respectively. The progeny of M. xiaojinensis × M. baccata comprised hybrids of 2x, 3x, 4x, or 5x ploidy, whereas apomictic offspring were 2x, 3x, or 4x. Among the apomictic derived progeny, the ploidy of restituted apomictic progeny was 2x, 3x, or 4x, whereas that of nonrestituted apomictic progeny was 4x only. The proportions of the different types of apomictic derived progeny differed among the years 2008 to 2010. The ploidy of progeny from emasculated flowers also segregated into 2x, 3x, and 4x individuals. These results indicate that both parthenogenesis and unreduced meiotic diplospory play important roles in apomictic reproduction in M. xiaojinensis.     

Multi-phenotype behavioral characterization of inbred strains derived from wild stocks of Mus musculus

Many aspects of mouse behavior have been studied by using only a relatively small sample of available laboratory strains. These laboratory mice were derived from the so-called ``fancy mouse' and in most cases underwent extensive domestication before inbreeding. Thus, the behavioral repertoire of the laboratory mouse may be very different from that exhibited by stocks that have not been deliberately domesticated. Another inherent problem in analyzing mouse behavior is that genetic diversity is limited among currently available strains. In this respect, the use of strains that are derived from a variety of wild mice should provide a means to identifying novel behavioral phenotypes. We have investigated several behavioral phenotypes, using females of a number of mouse strains derived from wild mice of different subspecies, BFM/2, NJL, BLG2, HMI, CAST/Ei, KJR, SWN and MSM; a strain derived from fancy mice, JF1; and two laboratory strains, C57BL/6 and DBA/1. In this report, tests for locomotor activity, light-dark transitions, passive and active avoidance, and nociception were conducted. The results show great diversity of behavioral patterns between strains in contrast to less within-strain variability. We also found that two strains, KJR and SWN, both have good learning ability, whereas BLG2 mice exhibit impairment in both passive and active avoidance learning. Received: 11 January 2000 / Accepted: 27 March 2000     

代表性差异分析技术与疾病基因的克隆

本文结合代表性差异分析的技术原理和方法,介绍了近年来该方法在肿瘤基因克隆、亲病原体的筛查和多态相关标志物的分离等方面的应用,并提出了存在的总是和今后的展望。