The relative importance of genetic and nongenetic inheritance in relation to trait plasticity in Callosobruchus maculatus

A trait's response to natural selection will reflect the nature of the inheritance mechanisms that mediate the transmission of variation across generations. The relative importance of genetic and nongenetic mechanisms of inheritance is predicted to be related to the degree of trait plasticity, with nongenetic inheritance playing a greater role in the cross‐generational transmission of more plastic traits. However, this prediction has never been tested. We investigated the influence of genetic effects and nongenetic parental effects in two morphological traits differing in degree of plasticity by manipulating larval diet quality within a cross‐generational split‐brood experiment using the seed beetle Callososbuchus maculatus. In line with predictions, we found that the more plastic trait (elytron length) is strongly influenced by both maternal and paternal effects whereas genetic variance is undetectable. In contrast, the less plastic trait (first abdominal sternite length) is not influenced by parental effects but exhibits abundant genetic variance. Our findings support the hypothesis that environment‐dependent parental effects may play a particularly important role in highly plastic traits and thereby affect the evolutionary response of such traits.     

Variation in generative cell plastid nucleoids and male fertility in Medicago sativa

Biparental inheritance of plastids has been documented in numerous angiosperm species. The adaptive significance of the mode of plastid inheritance (unior biparental) is poorly understood. In plants exhibiting paternal inheritance of plastids, DNA-containing plastids in the microgametophyte may affect survival or growth of the gametophyte or the embryo. In this study the number of plastids containing DNA (nucleoids) in generative cells and generative cell and pollen volumes were evaluated in a range of genotypes of Medicago sativa (alfalfa). M. sativa exhibits biparental inheritance of plastids with strong paternal bias. The M. sativa genotypes used were crossed as male parents to a common genotype and the relationships between the gametophytic traits measured and male reproductive success were assessed. Generative cell plastid number and pollen grain size exhibited opposing associations with male fertility. Path analysis showed that generative cell plastid number was negatively associated with male fertility. This study provides evidence that there may be a competitive advantage at fertilization afforded sperm that have minimized their organelle content. The apparent lack of strong selection for reduced plastid number in generative cells of M. sativa may be a reflection of the diminished importance of reproductive success due to its perenniality or its long use in cultivation.     

Segregation Analysis on Genetic System of Quantitative Traits in Plants

Based on the traditional polygene inheritance model of quantitative traits, the author suggests the major gene and polygene mixed inheritance model. The model was considered as a general one, while the pure major gene and pure polygene inheritance model was a specific case of the general model. Based on the proposed theory, the author established the segregation analysis procedure to study the genetic system of quantitative traits of plants. At present, this procedure can be used to evaluate the genetic effect of individual major genes (up to two to three major genes), the collective genetic effect of polygene, and their heritability value. This paper introduces how to establish the procedure, its main achievements, and its applications. An example is given to illustrate the steps, methods, and effectiveness of the procedure. Translated from Hereditas, 2005, 27(1) (in Chinese)     

Inheritance and segregation of exogenous genes in transgenic cotton

Three transgenic cotton varieties (lines) were chosen for the study of inheritance and segregation of foreign Bt (Bacillus thuringiensis toxin) andtfdA genes in cotton. The transformed cotton varieties CCRI 30 and NewCott 33B expressing the BtcryIA gene, and cotton line TFD expressing thetfdA gene were crossed with CCRI 19, CCRI 12 and Lumian 6. The results confirm inheritance and segregation of (i) the exogenous Bt gene in transgenic CCRI 30 and NewCott 33B, governing resistance to bollworm, and (ii) the exogenoustfdA gene in transgenic TFD, governing resistance to the herbicide 2,4-D. Both resistance characters were governed by a single dominant nuclear gene, and were not affected by cytoplasm. Our data support the conclusion that foreign traits encoded by single genes are inherited and expressed in Mendelian fashion in cotton. Our results also indicate that a practical backcross breeding program could be used to develop cotton cultivars combining one or more resistance traits from foreign and native gene sources.     

Paternal epigenetic effects of population density on locust phase‐related characteristics associated with heat‐shock protein expression

Many species exhibit transgenerational plasticity by which environmental cues experienced by either parent can be transmitted to their offspring, resulting in phenotypic variants in offspring to match ancestral environments. However, the manner by which paternal experiences affect offspring plasticity through epigenetic inheritance in animals generally remains unclear. In this study, we examined the transgenerational effects of population density on phase‐related traits in the migratory locust Locusta migratoria. Using an experimental design that explicitly controls genetic background, we found that the effects of crowd or isolation rearing on phase plasticity could be inherited to the offspring. The isolation of gregarious locusts resulted in reduced weight in offspring eggs and altered morphometric traits in hatchlings, whereas crowding of solitarious locusts exhibited opposite effects. The consequences of density changes were transmitted by both maternal and paternal inheritance, although the expression of paternal effects was not as pronounced as that of maternal effects. Prominent expression of heat‐shock proteins (Hsps), such as Hsp90, Hsp70 and Hsp20.6, could be triggered by density changes. Hsps were significantly upregulated upon crowding but downregulated upon isolation. The variation in parental Hsp expression was also transmitted to the offspring, in which the pattern of inheritance was consistent with that of phase characteristics. These results revealed a paternal effect on phase polyphenism and Hsp expression induced by population density, and defined a model system that could be used to study the paternal epigenetic inheritance of environmental changes.     

RFLP marker analysis supports tetrasonic inheritance in Lotus corniculatus L.

Lotus corniculatus is a tetraploid (2n=4x=24) perennial forage legume and has been reported to have tetrasomic inheritance for several traits, although it has also been reported to show disomic inheritance. Molecular markers were used to clarify whether tetrasomic inheritance, disomic inheritance, or a combination of both, was found within an F₂ population arising from a cross between two diverse L. corniculatus accessions. The inheritance of ”tetra-allelic” RFLP markers (markers with four segregating bands) indicated that disomic inheritance could not account for the phenotypic F₂ classes observed, and that only tetrasomic inheritance would explain the observed results. Goodness of fit tests for ”tetra-allelic” and ”tri-allelic” (three segregating bands) RFLP marker data suggested support for chromosomal-type tetrasomic inheritance. RFLP genotypes interpreted from autoradiographic signal intensity provided additional support for tetrasomic inheritance and the occurrence of preferential pairing between parental chromosomes. Bivalent pairing was predominant in the two parental lines and their F₁ hybrid in cytological analyses. L. corniculatus has been classified as both an autotetraploid and an allotetraploid species. RFLP evidence of tetrasomic inheritance gives support for L. corniculatus being classified as an autotetraploid species. Even though bivalent pairing occurs, as seen in other autotetraploid species, pairing between any of the four homologous chromosomes is possible. Preferential pairing in the F₁ hybrid suggests that genome differentiation appears to be minimal between homologs within an accession, while genome differentiation is greater between homologs from different accessions of this genetically diverse species. Received: 16 November 1999 / Accepted: 14 July 2000     

Critical Notice: Cycles of Contingency – Developmental Systems and Evolution

The themes, problems and challenges of developmental systems theory as described in Cycles of Contingency are discussed. We argue in favor of a robust approach to philosophical and scientific problems of extended heredity and the integration of behavior, development, inheritance, and evolution. Problems with Sterelny's proposal to evaluate inheritance systems using his `Hoyle criteria' are discussed and critically evaluated. Additional support for a developmental systems perspective is sought in evolutionary studies of performance and behavior modulation of fitness.     

A generalised approach to the study and understanding of adaptive evolution

Evolutionary theory has made large impacts on our understanding and management of the world, in part because it has been able to incorporate new data and new insights successfully. Nonetheless, there is currently a tension between certain biological phenomena and mainstream evolutionary theory. For example, how does the inheritance of molecular epigenetic changes fit into mainstream evolutionary theory? Is niche construction an evolutionary process? Is local adaptation via habitat choice also adaptive evolution? These examples suggest there is scope (and perhaps even a need) to broaden our views on evolution. We identify three aspects whose incorporation into a single framework would enable a more generalised approach to the understanding and study of adaptive evolution: (i) a broadened view of extended phenotypes; (ii) that traits can respond to each other; and (iii) that inheritance can be non-genetic. We use causal modelling to integrate these three aspects with established views on the variables and mechanisms that drive and allow for adaptive evolution. Our causal model identifies natural selection and non-genetic inheritance of adaptive parental responses as two complementary yet distinct and independent drivers of adaptive evolution. Both drivers are compatible with the Price equation; specifically, non-genetic inheritance of parental responses is captured by an often-neglected component of the Price equation. Our causal model is general and simplified, but can be adjusted flexibly in terms of variables and causal connections, depending on the research question and/or biological system. By revisiting the three examples given above, we show how to use it as a heuristic tool to clarify conceptual issues and to help design empirical research. In contrast to a gene-centric view defining evolution only in terms of genetic change, our generalised approach allows us to see evolution as a change in the whole causal structure, consisting not just of genetic but also of phenotypic and environmental variables.     

Non-mendelian inheritance of mitochondrial DNA and ribosomal DNA in the myxomycete, Didymium iridis

Summary The inheritance of both the mitochondrial DNA (mtDNA) and the nuclear-encoded extrachromosomal ribosomal DNA (rDNA) has been studied in the myxomycete, Didymium iridis, by DNA-DNA hybridization of labeled probes to total DNA at various stage of the life cycle. Both the mtDNA and rDNA populations rapidly become homogeneous in individuals, but there is a qualitative difference in the patterns of inheritance of these two molecules. One parental rDNA type was preferentially inherited in all crosses; selective replication of this molecule is tentatively proposed as the mechanism of inheritance. In contrast, either parental mtDNA type could be inherited. Since the inherited population of parental mtDNA molecules are not partitioned into cells in this coenocytic organism, no known mechanism of inheritance can explain the rapid and apparently random loss of one parental mtDNA type in individuals.     

Inheritance of mitochondrial and chloroplast genomes in the isogamous brown alga Scytosiphon lomentaria (Phaeophyceae)

Patterns of inheritance of chloroplasts and mitochondria were examined by fluorescence microscopy and haplotype genome markers in the isogamous brown alga Scytosiphon lomentaria (Lyngbye) Link. Germination of the zygote in this species was unilateral, the growing thallus developed entirely from the germ tube, and the original zygote cell did not develop except for the formation of a hair. Inheritance of chloroplasts was biparental, and partitioning of the two parental chloroplasts into the first sporophytic cells was accidental: either the maternal or the paternal chloroplast was migrated from the zygote into the germ tube cell, whereas the other chloroplast remained in the original cell. In contrast, the mitochondrial genome in all cells of the sporophyte came only from the female gamete (maternal inheritance). These inheritance patterns are similar to those of the isogamous brown alga Ectocarpus siliculosus (Dillwyn) Lyngbye. Maternal inheritance of mitochondria might be universal in brown algae.     

Genetics and hybridization in surface and cave Astyanax (Teleostei): a comparison of regressive and constructive traits

Change in ecological conditions, as seen in surface and cave populations of Astyanax (Teleostei), has caused the divergent evolution of a large number of traits like eyes, coloration, taste, lateral line, and different kinds of behaviour like schooling, sleep or feeding posture. Because of the interfertility of surface and cave forms these fish are an exceptional object to study the morphological and genetic basis of the evolution of such complex regressive and constructive traits. Classical crossing analyses and genomic studies are contributing to growing understanding. Both kinds of traits mostly rely on multiple genetic bases and the phenotypic manifestation in the various crosses is similar. The gene effect underlying the phenotypic manifestation may exhibit an exponential increase at differing amounts in the various traits and crosses. Missing or presence of such genetic interaction helps determine whether the variability of eyes or pigmentation exhibited by Astyanax cave fish populations like Micos, is due to a more recent origin or to secondary hybridization with the surface fish. Neither crossing analysis nor QTL mapping revealed that eye reduction is pleiotropically antagonistically related to the increase of taste buds or lateral line sense. Independent inheritance of traits suggests that Astyanax cave fish are subjected to mosaic evolution.     

Bridging the explanatory gaps: What can we learn from a biological agency perspective?

We begin this article by delineating the explanatory gaps left by prevailing gene-focused approaches in our understanding of phenotype determination, inheritance, and the origin of novel traits. We aim not to diminish the value of these approaches but to highlight where their implementation, despite best efforts, has encountered persistent limitations. We then discuss how each of these explanatory gaps can be addressed by expanding research foci to take into account biological agency—the capacity of living systems at various levels to participate in their own development, maintenance, and function by regulating their structures and activities in response to conditions they encounter. Here we aim to define formally what agency and agents are and—just as importantly—what they are not, emphasizing that agency is an empirical property connoting neither intention nor consciousness. Lastly, we discuss how incorporating agency helps to bridge explanatory gaps left by conventional approaches, highlight scientific fields in which implicit agency approaches are already proving valuable, and assess the opportunities and challenges of more systematically incorporating biological agency into research programs.     

Paternal inheritance of plastids in interspecific hybrids of the genus Actinidia revealed by PCR-amplification of chloroplast DNA fragments

RFLPs (restriction fragment length polymorphisms) of PCR (polymerase chain reaction) -amplified fragments were used to trace the pattern of plastid DNA inheritance in the genus Actinidia. A total of 51 progeny originating from interspecific crosses between three A. arguta cultivars and A. deliciosa, the kiwifruit, and 12 progeny originating from the cross between A. kolomikta and A. chinensis were analysed together with their parents. No reciprocal crosses could be tested since they all failed to set viable seeds. Attempts to rescue immature embryos failed in all cases as well. The A. arguta×A. deliciosa crosses were checked for the RFLP patterns of a sequence encoding part of the Rubisco large subunit (rbcL), using either AluI or MseI, and for a sequence encoding part of the photosystem II D1 protein (psbA), using HinfI. The A. kolomikta×A. chinensis cross was checked for the RFLP patterns of sequences encoding the spacers between trnT and the 5-trnL exon (a-b spacer DNA) and the trnL 3 exon and trnF (e-f spacer DNA), respectively. The first spacer revealed a natural polymorphism between the two parent species due to a large deletion occurring in A. kolomikta detectable without further restriction enzyme treatment. The e-f spacer DNA was digested with HinfI. The comparison of the RFLP patterns in the parents and their progeny showed a strictly paternal inheritance of chloroplast DNA in Actinidia, with no exception found in any of the crosses examined. As the reciprocal crosses were not available, we do not know whether paternal inheritance of plastids is restricted to the crosses we analysed or if this is the general rule for plastid inheritance in the genus Actinidia. Actinidia is dioecious and is the first purely outbreeding species for which a paternal plastid inheritance has so far been documented.     

Evolution of a Unique Mitotype-Specific Protein-Coding Extension of the Cytochrome c Oxidase II Gene in Freshwater Mussels (Bivalvia: Unionoida)

A unique mode of mitochondrial DNA inheritance, designated doubly-uniparental inheritance (DUI), occurs in three bivalve subclasses (Pteriomorpha: Mytiloida, Palaeoheterodonta: Unionoida, Heterodonta: Veneroida), indicating that DUI may be a widespread phenomenon among bivalves. In mytiloids, breakdown of this pattern of inheritance (gender-switching) is observed in natural populations and in a phylogenetic context. In contrast, gender-switching has not occurred during the evolutionary history of unionoids. Here we present sequences for the male (M) and female (F) mitotypes from an additional 8 species of Unionoida. Consistent with previous observations, the M and F mitotypes of all species form reciprocally monophyletic clades supporting the hypothesis of taxon-specific rates of gender-switching. Coinciding with the absence of gender-switching is an ≈185 codon extension of the cytochrome c oxidase II (MTCO2) locus in the male genome. The extension is present in all 12 unionoid species examined, including a representative of the family Margaritiferidae, indicating that this protein-coding polymorphism originated ≥ 200 MYBP. Although the extension is well conserved in length among 11 of the 12 species, one taxon has a significantly shortened extension. Lastly, examination of the rates and patterns of substitution indicate that the extension is evolving under relaxed purging selection, a pattern inconsistent with the conserved nature of MTCO2 or any cytochrome c oxidase locus.[Reviewing Editor: Dr. J. William Ballard]     

Incomplete paternal inheritance of chloroplast DNA recognized in Chamaecyparis obtusa using an intraspecific polymorphism of the trnD-trnY intergenic spacer region

Using a fluorescence-based PCR-SSCP (single-strand conformation polymorphism), we verified imperfectibility in the paternal inheritance of chloroplast DNA (cpDNA) in Chamaecyparis obtusa (Cupressaceae) controlled crosses. An intraspecific sequence polymorphism of the intergenic spacer region between the trnD and trnY genes was utilized as a molecular marker. Of 361 progenies, in which the cpDNA haplotypes of their female and male parents were different, 352 (97.5%) possessed the same haplotypes as their male parents, and nine (2.5%) the same haplotypes as their female parents. The parentage of the nine progenies with female parental types was diagnosed using DNA fingerprinting based on fluorescence-based RAPD profiles. Their parentage showed convincing evidence of the low frequency of maternal inheritance. Moreover, heteroplasmy was observed in the open-pollinated seeds collected in a seed orchard. The confirmation of maternal plastid transmission in the full-sib families and the observation of heteroplasmy in seeds reveal that the paternal inheritance of cpDNA is not an exclusive phenomenon and that the mode of its inheritance is biparental in C. obtusa. Received: 15 April 2000 / Accepted: 13 July 2000     

Revisiting telegony: offspring inherit an acquired characteristic of their mother's previous mate

Newly discovered non‐genetic mechanisms break the link between genes and inheritance, thereby also raising the possibility that previous mating partners could influence traits in offspring sired by subsequent males that mate with the same female (‘telegony’). In the fly Telostylinus angusticollis, males transmit their environmentally acquired condition via paternal effects on offspring body size. We manipulated male condition, and mated females to two males in high or low condition in a fully crossed design. Although the second male sired a large majority of offspring, offspring body size was influenced by the condition of the first male. This effect was not observed when females were exposed to the first male without mating, implicating semen‐mediated effects rather than female differential allocation based on pre‐mating assessment of male quality. Our results reveal a novel type of transgenerational effect with potential implications for the evolution of reproductive strategies.     

Segregation Analysis on Genetic System of Quantitative Traits in Plants

Based on the traditional polygene inheritance model of quantitative traits,the author suggests the major gene and polygene mixed inheritance model.The model was considered as a general one,while the pure major gene and pure polygene inheritance model was a specific case of the general model.Based on the proposed theory,the author established the segregation analysis procedure to study the genetic system of quantitative traits of plants.At present,this procedure can be used to evaluate the genetic effect of individual major genes (up to two to three major genes),the collective genetic effect of polygene,and their heritability value.This paper introduces how to establish the procedure,its main achievements,and its applications.An example is given to illustrate the steps,methods,and effectiveness of the procedure.     

转基因棉花外源基因的遗传

选用不同来源的转Bt基因抗虫棉中棉所30号和新棉33B、转tfdA基因抗除草剂棉花材料TFD,通过与不同主栽推广品种正反交,研究了外源Bt基因和tfdA基因在棉株体内的遗传和分离行为。结果表明,由于外源基因提供给转基因棉花的抗虫和抗除草剂性状均是由一对于基因控制的显性性状,且该性状不受细胞质效应的影响,符合孟德尔遗传规律。     

Preferential degradation of plastid DNA with preservation of mitochondrial DNA in the sperm cells ofPelargonium zonale during pollen development

Summary In the present study, we studied changes in organellar DNA in the sperm cells of maturing pollen ofPelargonium zonale, a plant typical to exhibit biparental inheritance, by fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI) and by immunogold electron microscopy using anti-DNA antibody. Fluorescence intensities of DAPI-stained plastid nuclei in generative and sperm cells at various developmental stages were quantified with a video-intensified microscope photon counting system (VIMPCS). Results indicated that the amount of DNA per plastid in generative cells increased gradually during pollen development and reached a maximum value (about 70 T per plastid; 1 T represents the amount of DNA in a particle of T4 phage) in young sperm cells at 5 days before flowering. However, the DNA content of plastids was subsequently reduced to about 20% of the maximum value on the day of flowering. Moreover, the DNA content of the plastid further decreased to 4% of the maximum value when pollen grains were cultured for 6 h in germination medium. In contrast, the amount of DNA per mitochondrion did not decrease significantly around the flowering day. Similar results were also obtained by immunogold electron microscopy using anti-DNA antibody. The density of gold particles on plastids decreased during pollen maturation whereas labelling density on mitochondria remained relatively constant. The number of plastids and mitochondria per generative cell or per pair of sperm cells did not change significantly, indicating that the segregation of DNA by plastid division was not responsible for the decrease in the amount of DNA per plastid. These results indicate that the plastid DNA is preferentially degraded, but the mitochondrial DNA is preserved, in the sperm cells ofP. zonale. While the plastid DNA of the sperm cells decreased before fertilization, it was also suggested that the low DNA contents that remain in the plastids of the sperm cells are enough to account for the biparental inheritance of plastids inP. zonale.Abbreviations DAPI 4,6-diamidino-2-phenylindole - VIMPCS video-intensified microscope photon counting system     

Autophagy is not involved in the degradation of sperm mitochondria after fertilization in mice

In almost all animals, mitochondrial DNA (mtDNA) is transmitted only from the female, while the paternal mitochondria and mtDNA are thought to be eliminated during early embryogenesis. Autophagy is involved in the elimination of sperm mitochondria and mtDNA in early embryos in Caenorhabditis elegans; however, solid evidence is still lacking in mammals. Recently, we found that despite the fact that some autophagy-related proteins, such as SQSTM1 and LC3 could localize nearby sperm mitochondria before the 2-cell stage, autophagy did not participate in the elimination of sperm mitochondria and mtDNA. Instead, the pre-elimination of sperm mtDNA before fertilization and the restriction of sperm mitochondria in one blastomere before 4-cell stage embryos are the most important mechanisms of maternal mitochondrial inheritance in mice.