Inheritance of chromosome length polymorphisms inCoprinus cinereus

The sexually compatible strains ofCoprinus cinereus 5302 and Dd 13 revealed chromosome length polymorphisms in their electrophoretic karyotypes. The dikaryon derived from two monokaryons contained a mixture of the two electrophoretic patterns. F₁ progenies were isolated by crossingC. cinereus 5302 and Dd 13 strains and it showed unique karyotypes. Chromosome length polymorphisms of both parental strains were inherited at random in the F₁ progenies. As a result, several novel electrophoretic karyotypes which had not been observed in either parental strains were found in the F₁ progeny. The rDNA probe hybridized with one chromosome in both parental strains, with two chromosomes in the hybridization pattern of both parental strains in the dikaryon, and with one to two chromosomes in the F₁ progenies. The relation between mating type and hybridization pattern has thus not been made clear in the case of F₁ progeny.     

Behavior of chromosomes after meiosis inCoprinus cinereus

The movement was investigated of a specific chromosome in the F₁ progeny of the basidiomyceteCoprinus cinereus. We focussed our attention on the smallest chromosome of the 5302 strain. We first constructed a chromosome-smallest library and screened it with a chromosome-specific clone, pRC 1. The pRC 1 probe hybridized only with the smallest chromosome of the 5302 strain, and it detected one band of different mobility in two parental strains. In the F₁ progeny, the probe hybridized with one to three chromosomes. Most of the hybridized chromosomes in the F₁ progeny were positioned in terms of mobility between the hybridized chromosomes of the two parental strains. Therefore, they were probably generated by meiotic recombination between homologous chromosomes of different sizes.     

SEXUAL SELECTION AGAINST HYBRIDS BETWEEN SYMPATRIC STICKLEBACK SPECIES: EVIDENCE FROM A FIELD EXPERIMENT

Sexual selection against viable, fertile hybrids may contribute to reproductive isolation between recently diverged species. If so, then sexual selection may be implicated in the speciation process. Laboratory measures of the mating success of hybrids may underestimate the amount of sexual selection against them if selection pressures are habitat specific. Male F₁ hybrids between sympatric benthic and limnetic sticklebacks (Gasterosteus aculeatus complex) do not suffer a mating disadvantage when tested in the laboratory. However, in the wild males choose different microhabitats and parental females tend to be found in the same habitats as conspecific males. This sets up the opportunity for sexual selection against male hybrids because they must compete with parental males for access to parental females. To test for sexual selection against adult F₁ hybrid males, we examined their mating success in enclosures in their preferred habitat (open, unvegetated substrate) where limnetic males and females also predominate. We found significantly reduced mating success in F₁ hybrid males compared with limnetic males. Thus, sexual selection, like other mechanisms of postzygotic isolation between young sister species, may be stronger in a wild setting than in the laboratory because of habitat-specific selection pressures. Our results are consistent with, but do not confirm, a role for sexual selection in stickleback speciation.     

Molecular studies of FIme resistance plasmids, particularly in epidemic Salmonella typhimurium.

Summary The molecular sizes of F₁ me resistance plasmids from strains of Salmonella typhimurium, S. wien and S. typhi were within the range 87.9–102.6×10⁶ daltons. DNA reassociation studies indicated that the plasmids from these hosts had at least 80% of their nucleotide sequences in common. A high proportion of F₁ me plasmids cannot mediate their own transfer. The non-autotransferring property of such plasmids is the result of DNA deletion; a non-autotransferring F₁ me plasmid was about 10×10⁶ daltons shorter than autotransferring representatives of the group, and its DNA showed 100% homology with them. Plasmids of the F₁ me group are incompatible with the F factor and with F₁R factors. F₁ me plasmids are incompatible with the fi ⁺ MP10 plasmid of S. typhimurium, whereas F and F₁ factors are compatible with MP10 (Anderson et al., 1977). There was no significant DNA homology between members of the F₁ me group and MP10, and these plasmids may share only a small region of DNA responsible for their incompatibility. The F₁ me R factors examined had 29–37% DNA homology with the F factor, and 50–58% homology with the F₁ resistance plasmid, R162. Molecular examination therefore supports the genetic differentiation of members of the F₁ me group from other F-like plasmids. Both types of investigation can thus be used in epidemiological studies of bacterial strains carrying resistance or other plasmids.     

Airborne‐pollen pool and mating pattern in a hybrid zone between Pinus pumila and P. parviflora var. pentaphylla

The reproductive isolation barriers and the mating patterns among Pinus pumila, P. parviflora var. pentaphylla and their hybrids were examined by flowering phenology and genetic assays of three life stages: airborne‐pollen grains, adults and seeds, in a hybrid zone on Mount Apoi, Hokkaido, Japan. Chloroplast DNA composition of the airborne‐pollen was determined by single‐pollen polymerase chain reaction. Mating patterns were analysed by estimating the molecular hybrid index of the seed parent, their seed embryos and pollen parents. The observation of flowering phenology showed that the flowering of P. pumila precedes that of P. parviflora var. pentaphylla by about 6 to 10 days within the same altitudinal ranges. Although this prezygotic isolation barrier is effective, the genetic assay of airborne‐pollen showed that the two pine species, particularly P. pumila, still have chances to form F₁ hybrid seeds. Both parental species showed a strong assortative mating pattern; F₁ seeds were found in only 1.4% of seeds from P. pumila mother trees and not at all in P. parviflora var. pentaphylla. The assortative mating was concluded as the combined result of flowering time differentiation and cross‐incompatibility. In contrast to the parental species, hybrids were fertilized evenly by the two parental species and themselves. The breakdown of prezygotic barriers (intermediate flowering phenology) and cross‐incompatibility may account for the unselective mating. It is suggested that introgression is ongoing on Mount Apoi through backcrossing between hybrids and parental species, despite strong isolation barriers between the parental species.     

Mating preferences of F2 segregants of crosses between MHC-congenic mouse strains

Male and female F₂ homozygotes from crosses between MHC-congenic inbred mouse strains were tested for MHC-associated mating preference. In three instances, of the four genotypic combinations so tested, marked MHC-associated mating preference was observed. This result greatly reduces the possibility that the observed mating preferences of MHC-congenic inbred strains can be explained wholly in terms of non-MHC genetic drift, or of residual non-MHC genetic disparity, or of fortuitous acquired strain characteristics unrelated to MHC. In two of the four combinations investigated, the MHC-related mating bias of F₂ segregants was similar to that of the genotypically similar inbred parent strains. In a third combination, F² segregants did not show the mating bias exhibited by the corresponding parent strains. In a fourth combination, F₂ segregants displayed an MHC-related mating bias that was evident in the corresponding parental inbred strains only when the colonies of the parent strains had been maintained in isolation from other strains. While the exhibition of mating preference by mice of the same genotypes may differ according to circumstances, as indicated, in no instance was preference reversed. Mating preference in a given combination of MHC genotypes, whenever it was observed, always favored the same MHC haplotype of the two alternative haplotypes represented. It appears that the familial MHC genotypes of mice and the environment in which the colonies are maintained influence their MHC-related mating preference, but it has yet to be decided whether these factors operate by determining exposure to particular MHC haplotypes.Abbreviations used in this paper are as follows B6 C57BL/6 - B10 C57BL/10 - BALE BALB/c - BALB.B BALB.B10 - INB inbred - MHC major histocompatibility complex See also Figure 1     

Safety of a novel oxygen-coordinated niacin-bound chromium(III) complex (NBC): I. Two-generation reproduction toxicity study

The objective of this study was to evaluate the effects of a novel oxygen-coordinated niacin-bound chromium(III) complex (NBC) on the reproductive systems of male and female rats, the postnatal maturation and reproductive capacity of their offspring, and possible cumulative effects through multiple generations. Sprague-Dawley rats were maintained on feed containing NBC at dose levels of 0, 4, 15, or 60 ppm for 10 weeks prior to mating, during mating, and, for females through gestation and lactation, across two generations. For the parents (F₀ and F₁) and the offspring (F₁ and F_2a), reproductive parameters such as fertility and mating, gestation, parturition, litters, lactation, sexual maturity and development of offspring were assessed. Results from the current study indicated that dietary exposure of NBC to parental male and female rats of both (F₀ and F₁) the generations during the premating and mating periods, for both sexes, and during gestation and lactation in case of female rats, did not cause any significant incidence of mortality or abnormal clinical signs. Compared to respective controls, NBC exposure did not affect reproductive performance as evaluated by sexual maturity, fertility and mating, gestation, parturition, litter properties, lactation and development of the offspring. Based on the findings of this study, the parental as well as the offspring no-observed-adverse-effect level for NBC was determined to be greater than 60 ppm in diet or equivalent to 7.80 and 8.31 mg/kg body weight/day in male and female rats, respectively.     

Cyclophosphamide-Induced IN VIVO Sister Chromatid Exchanges (Sce) in MUS MUSCULUS. III. Quantitative Genetic Analysis

In vivo cyclophosphamide (CP)-induced sister chromatid exchanges (SCEs) were evaluated in females from five genetic strains of mice (C57BL/6J, C3H/S, 129/ReJ, BALB/c and DBA/2) and their F₁ hybrids. Baseline (noninduced) SCE values differ significantly among strains, 129/ReJ having the lowest and DBA/2 having the highest mean SCE per cell values. In general, the baseline SCE of a given F₁ is within the range of its corresponding parental strains or near the lower parental value. Furthermore, there is a genotype-dependent increase in mean SCEs per cell with CP dose. Strain differences in SCE induction are noted particularly at the two higher CP doses (4.50 and 45.0 mg/kg). In general, F₁ hybrids involving a strain with high induced SCEs and a strain with low induced SCEs exhibit mean SCE values that are closer to the value of the lower strain. F₁ s involving two strains with high SCEs or two strains with low SCEs yield SCEs not different from parental strains. The method of diallel cross analysis showed the order of dominance of these strains in SCE induction to be 129/ReJ BALB/c C3H/S DBA/2 C57BL/6J. These results support the involvement of predominantly nonadditive genetic factors as major gene(s) in SCE induction. In addition, involvement of random and independent events in SCE induction is suggested by the distribution of SCEs which follows a Poisson distribution.     

H-2-associated differences in androgen-influenced organ weights of a and C57BL/10 mouse strains and their crosses

The influence ofH-2 haplotypes (in three-month-old males) on body weight, vesicular gland, testes, and thymus weight was investigated in A, B10, and B10.A strains and their respective F₁, F₂, and Bc progeny. The influence of theH-2 haplotypes was found to contribute to heterosis in the body weight.H-2 ^a/H-2 ^a males have a smaller vesicular gland and larger testes and thymus weight thanH-2 ^b/H-2 ^b males when groups with an identical or comparable genetic background are compared.H-2 heterozygous classes are closer to the parental strain with higher values for absolute organ weight; for relative organ weight, the heterozygous classes are intermediate or closer to the parental strain with lower values. This complex situation results from the simultaneous action ofH-2 haplotypes on both organ weight (Hom-1 effect) and body weight (heterosis), which probably operate through different mechanisms. Coat color genes were found to modify the penetrance ofH-2 influence on quantitative traits.     

Template mixing: a method of enhancing detection and interpretation of codominant RAPD markers

Ten codominant RAPD markers, ranging in size from about 300 to about 1350 bp, were identified in mapping populations of chickpea (Cicer arietinum L.) and diploid strawberry (Fragaria vesca L.). A distinguishing feature of all ten markers, and perhaps of codominant RAPD markers in general, was the presence in heterozygous individuals of a non-parental, heteroduplex band migrating more slowly than either of the respective parental bands. This non-parental band could also be generated by mixing parental DNAs before PCR (template mixing). As a means of identifying primers likely to detect codominant RAPD markers, parental and mixed-template (parent-parent) PCR-product gel lanes were compared for 20 previously untested RAPD primers (10-base oligomers). Four primers that produced a total of five non-parental, heteroduplex bands in mixed-template reactions were selected, and then used to detect a total of five segregating, codominant markers and nine dominant markers in the respective F₂ mapping population, a codominant marker frequency of 35.7%. When closely migrating fast and slow bands of codominant RAPDs were difficult to differentiate, parent-progeny template mixing was used to deliberately generate heteroduplex bands in fast- or slow-band F₂ homozygotes, respectively, allowing confirmation of marker phenotype.     

Linkage disequilibrium in crosses between Illinois maize strains divergently selected for protein percentage

The objectives of this study were two fold: (1) to determine whether divergent selection for kernel protein concentration, which produced the Illinois high protein (IHP), Illinois low protein (ILP), reverse low protein (RLP), and reverse high protein (RHP) maize (Zea mays L.) strains, had generated coupling-phase linkages among genes controlling protein concentration or other traits and (2) to measure the effectiveness of random mating in reducing linkage disequilibrium in segregating generations from crosses between the strains. To achieve these objectives, design III progenies from the F₂ and F₆ (produced by random mating the F₂) from the crosses of IHP × ILP, IHP × RHP, ILP × RLP, and RHP × RLP were evaluated. Estimates of additive variance for percent protein in the crosses of IHP × ILP and ILP × RLP were significantly less in the F₆ than in the F₂ indicating the presence of coupling-phase linkages in the parents and their breakup by random mating. In addition, a significant reduction in dominance variance for grain yield from the F₂ to the F₆ in IHP × ILP suggested the presence of repulsion-phase linkages. No other evidence of coupling or repulsion-phase linkages was found for any of the traits measured. These results demonstrate the effectiveness of long-term divergent selection in the development of coupling-phase linkages and of random mating to dissipate linkage disequilibrium.Research supported by the Illinois Agricultural Experiment Station     

Influences of inbreeding and genetics on telomere length in mice

We measured telomere lengths of blood leukocytes in several inbred and outbred mammalian species, using a telomere-specific fluorescent probe and flow cytometry. Humans, non-human primates, and three outbred populations of Peromyscus mice (Peromyscus leucopus, Peromyscus maniculatus, and Peromyscus polionotus) have short telomeres. Two common strains of laboratory mice, C57BL/6J and DBA/2J, have telomeres several times longer than most other mammals surveyed. Moreover, the two inbred laboratory mouse strains display significantly different telomere lengths, suggesting the existence of strain-specific genetic determinants. To further examine the effects of inbreeding, we studied three Peromyscus leucopus inbred lines (GS109, GS16A1, and GS16B), all derived from the outbred P. leucopus stock. Telomeres of all three inbred lines are significantly lengthened relative to outbred P. leucopus, and the three lines display strain-specific significantly different telomere lengths, much like the C57BL/6J and DBA/2J strains of M. musculus. To further characterize the genetic inheritance of telomere length, we carried out several crosses to obtain hybrid F₁ mice between parental strains displaying the phenotype of long and short telomeres. In all F₁ mice assayed, peripheral blood leukocyte telomere length was intermediate to that of the parents. Additionally, we generated F₂ mice from a cross of the (P. leucopus outbred × GS16B)F₁. Based on the distribution of telomere length in the F₂ population, we determined that more than five loci contribute to telomere length regulation in Peromyscus. We concluded that inbreeding, through unknown mechanisms, results in the elongation of telomeres, and that telomere length for a given species and/or sub-strain is genetically determined by multiple segregating loci.     

Genetic interactions between wheat and rye genomes in triticale

Summary Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F₁ exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F₁s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F₁s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F₁s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.     

THE GENETIC BASIS OF SEXUAL ISOLATION BETWEEN DROSOPHILA MELANOGASTER AND D. SIMULANS

The genetic analysis of sexual isolation between the closely-related species Drosophila melanogaster and Drosophila simulans involved two experiments with no-choice tests. The efficiency of sexual isolation was measured by the frequency of courtship initiation and interspecific mating. We first surveyed the variation in sexual isolation between D. melanogaster strains and D. simulans strains of different geographic origin. Then, to investigate variation in sexual isolation within strains, we made F₁ diallel sets of reciprocal crosses within strains of D. melanogaster and D. simulans. The F₁ diallel progeny of one sex were paired with the opposite sex of the other species. The first experiment showed significant differences in the frequency of interspecific mating between geographic strains. There were more matings between D. simulans females and D. melanogaster males than between D. melanogaster females and D. simulans males. The second experiment uncovered that the male genotypes in the D. melanogaster diallel significantly differed in interspecific mating frequency, but not in courtship initiation frequency. The female genotypes in the D. simulans diallel were not significantly different in courtship initiation and interspecific mating frequency. Genetic analysis reveals that in D. melanogaster males sexual isolation was not affected by either maternal cytoplasmic effects, sex-linked effects, or epistatic interaction. The main genetic components were directional dominance and overdominance. The F₁ males achieved more matings with D. simulans females than the inbred males. The genetic architecture of sexual isolation in D. melanogaster males argues for a history of weak or no selection for lower interspecific mating propensity. The behavioral causes of variation in sexual isolation between the two species are discussed.     

The genetic basis of non-disjunction: Increased incidence of hyperploidy in oocytes from F1 hybrid mice

Summary Oocytes from parental mice strains NMRI/Han, C57/bl and Balb/c and from F₁ hybrid lines were analysed for aneuploidy due to non-disjunction after gonadotropin-stimulated ovulation. No hyperploid oocytes were present in five of the strains studied. F₁ hybrids from crosses of NMRI/HanxC57/bl did ovulate, however, a significantly increased number of hyperploid oocytes, although females from their parental strains show a rather low incidence of non-disjunction. The evidence for a genetic basis for non-disjunction is assessed and possible causative factors are discussed.Dedicated to Professor Dr.P.E. Becker on the occasion of his 75th birthday     

Genetic control of seed proteins in wheat

Summary Electrophoretic profiles of crude protein extracts from seed of F₁ hybrids and reciprocal crosses among diploid, tetraploid and hexaploid wheats were compared with those of their respective parental species. The electrophoretic patterns within each of three pairs of reciprocal crosses, T.boeoticum X T.urartu, T.monococcun X T. urartu and T.dicoccum X T. araraticum, were different from one another but were identical with those of their respective maternal parents. Protein bands characteristic of the paternal parents were missing in F₁ hybrid seed suggesting that the major seed proteins in wheat were presumably regulated by genotype of the maternal parent rather than by the seed genotype. However, in another three pairs of reciprocal crosses, T.boeoticum X T. durum, T.dicoccum X T.aestivum and T. zhukovskyi x T. aestivum, protein bands attributable to the paternal parents were present in the F₁ hybrid seeds indicating that the seed proteins were not always exclusively regulated by the maternal genotype. The expression of paternal genomes is presumably determined by dosage and genetic affinity of the maternal and paternal genomes in the hybrid endosperm. The maternal regulation of seed protein content is probably accomplished through the maternal control over seed size. The seed protein quality may, however, depend upon the extent of expression of the paternal genome.     

Pollinator behaviour and the evolution of Louisiana iris hybrid zones

Pollinator preference may influence the origin and dynamics of plant hybrid zones. Natural hybrid populations between the red‐flowered Iris fulva and the blue‐flowered Iris brevicaulis are found in southern Louisiana. The genetic structure of these populations reflects a lack of intermediate genotypes. We observed pollinator behaviour in an experimental array with five plants each of I. fulva, I. brevicaulis, their F₁, and the first backcross generation in each direction, to obtain data on flower type preferences and transitions between flower types. The most abundant visitors were Ruby‐throated Hummingbirds (Archilochus colubris) and workers of the bumblebee Bombus pennsylvanicus. Hummingbirds visited I. fulva twice as often as I. brevicaulis and visited hybrids at intermediate frequencies. Bumblebee workers preferred the purple‐flowered F₁s and visited plants of I. fulva and the backcross to I. fulva more often than I. brevicaulis and its backcross. Overall, F₁ flowers were visited most frequently. Both hummingbirds and bumblebees visited nearest neighbours in almost 80% of the interplant movements. This meant that a majority of movements were between different flower types, rather than between plants of the same type. Findings from the present study suggest that pollinator preference is not a major causal factor for the lack of intermediate genotypes in natural iris hybrid populations. Instead, pollinator behaviour in our array promoted mixed mating between flower types belonging to different pollination syndromes. However, owing to predominant nearest‐neighbour visitation, the spatial distribution of parental and hybrid genotypes (in concert with pollinator behaviour) will have a strong influence on mating patterns and thus the genotypic structure and evolution of Louisiana iris hybrid zones.     

Genome shuffling amplifies the carbon source spectrum and improves arachidonic acid production in Diasporangium sp.

The aim of this study was to develop a new fungal strain that simultaneously amplifies the carbon source spectrum and increases arachidonic acid (AA) productivity using genome shuffling between Diasporangium sp. and inactive Aspergillus niger. Through three rounds of genome shuffling, one of the stable daughter strains (F₁) acquired the ability to produce arachidonic acid and utilize various carbon sources. Compared to the parental Diasporangium sp., which could only use four out of eight carbon sources tested, F₁ could utilize all eight carbon sources. During fermentation with CMC-Na as the carbon source, F₁ was able to obtain 30.16% of lipid effectively whereas the parental Diasporangium sp. was not able to grow at all. When glucose was used as the carbon source, the CMCase activity of F₁ was 879.36 U, 298.23% higher than that of the parental Diasporangium sp. Under optimized fermentation conditions in a 5-L fermentation container, the AA yield of F₁ reached 0.81 g/l, 94.78% higher than that of the parental generation. These results indicate that inter-kingdom genome shuffling can be used successfully in eukaryotic microorganisms and that it can effectively improve the production of desired metabolites within a short period of time. The findings of this study may be useful for extending the application of genome shuffling in eukaryotic microbial breeding.     

Genetic differences in wild strains of <Emphasis Type="Italic">Lentinula edodes</Emphasis> collected from a single fallen tree

Genetic differences among 18 Lentinula edodes strains isolated from a fallen trunk of Quercus mongolica var. grosseserrata were characterized by mating tests and restriction fragment length polymorphism (RFLP) analyses of mitochondrial DNA (mtDNA). These strains could be divided into six genets of different mating types. Because the mtDNA of the 18 strains showed four different RFLP genotypes, these strains seemed to have originated from at least 4 distinct parental strains. Strains belonging to the same genet were collected from fruiting bodies located not more than about 1m apart on the fallen tree. Implications of these findings regarding the degree of genetic variation and territory sizes of individual genets of wood-decaying basidiomycetes such as L. edodes are discussed.