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1.
SYNOPSIS. Thirty-one stocks of a marine ciliate, Euplotes minuta Yocom, collected from different localities, can be grouped in seven mating types. True pairs are formed only in mixtures of stocks belonging to different mating types. No selfing pairs or intraclonal conjugation have ever been observed. Synclonal inheritance of mating types is the rule, although about 10% of pairs show clonal inheritance. The latter can be explained by assuming syncaryon formation through cytogamy or through caryogamy of pronuclei derived from different products of meiosis. Mating type determination is due to 7 alleles at the single locus mt . There is complete dominance among the 7 alleles which can be orderly seriated, as shown in Table 3, according to their dominance relationship. The 5 stocks, and only these 5, of mating type VII have the autogamy trait. The mortality rate in F1 and F2 is very low–a maximum of 10%; however, the F2'S obtained by autogamy from F1 progenies in which mating type VII is involved have a very high mortality rate. The two facts (high mortality rate in F2 and strict association of autogamy trait with mating type VII in natural populations) have been considered as evidences of a probable isolation mechanism existing between mating type VII and the other 6 mating types. Thus, the 7 mating types have been assigned to the same syngen only tentatively.  相似文献   

2.
Supernatant malate dehydrogenase (MDH) isozymes (as visualized by starch gel electrophoresis) are encoded by two distinct gene loci in both the largemouth and smallmouth bass. When an interspecific F1 hybrid is formed between these two fish, a unique MDH isozyme is generated. The results of freeze-thaw molecular hybridization (which is the first application of this technique to MDH) indicate that this unique isozyme in the F1 hybrid is a heterodimer composed of one subunit of each parental type. The F1 hybrids produced F2 hybrids which in turn formed the F3 hybrid population. The inheritance of alleles at the MDH-B locus is consistent with a single Mendelian autosomal locus. Furthermore, there is no evidence of linkage between the lactate dehydrogenase-E locus and the MDH-B locus.  相似文献   

3.
To characterize the genetic basis of voluntary calcium consumption, we tested C57BL/6J mice (B6; with low avidity for calcium), PWK/PhJ mice (PWK; with high avidity for calcium) and their F1 and F2 hybrids. All mice received a series of 96-h two-bottle preference tests with a choice between water and the following: 50 m m CaCl2, 50 m m calcium lactate, 50 m m MgCl2, 100 m m KCl, 100 m m NH4Cl, 100 m m NaCl, 5 m m citric acid, 30 μ m quinine hydrochloride and 2 m m saccharin. Most frequency distributions of the parental and F1 but not F2 groups were normally distributed, and there were few sex differences. Reciprocal cross analysis showed that B6 × PWK F1 mice had a non-specific elevation of fluid intake relative to PWK × B6 F1 mice. In the F2 mice, trait correlations were clustered among the divalent salts and the monovalent chlorides. A genome screen involving 116 markers showed 30 quantitative trait loci (QTLs), of which six involved consumption of calcium chloride or lactate. The results show pleiotropic controls of calcium and magnesium consumption that are distinct from those controlling consumption of monovalent chlorides or exemplars of the primary taste qualities.  相似文献   

4.
Y. Gong  Q. Yang  S. Li  Y. Feng  C. Gao  G. Tu  X. Peng 《Animal genetics》2010,41(1):105-108
Based on the observation of a grey phenotype in the F1 generation from a cross between two white plumage duck varieties, the white Kaiya and the white Liancheng , we hypothesized a possible interaction between two autosomal loci that determine grey plumage. Using the parental and F1 individuals, seven testing combinations including five different F1 intercrosses (F2) and two different backcrosses (BC1 and BC2) were designed to test our hypothesis. It was demonstrated by chi-squared analysis that six test matings produced offspring in the expected ratios between the grey and white, with P- values ranging from 0.50 to 0.99. Another mating, where all white offspring were expected, produced 33 white individuals. These results verified that the interaction between two loci produced the grey phenotype. The C locus, which carries the recessive allele ( c ), was previously thought to be the only gene responsible for white plumage in the duck. This is the first report that an allele ( t ), carried by the white Liancheng at a different autosomal locus, also determines white plumage in ducks. Furthermore, the dominant alleles at both loci can interact with each other to produce the grey phenotype, and a new dark phenotype, observed in some F2 individuals, can be attributed to the dosage effect of the T allele.  相似文献   

5.
Abstract Cell-free extracts of Methanobacterium thermoautotrophicum (strain ΔH) converted the 8-OH-5-deazaflavin coenzyme F420 to factor 390, a 8-adenylyl derivative (F420-AMP). Activity was only observed upon exposure of the crude cell-free extract to oxygen. The ability to synthesize F390 was lost when crude cell-free extract was subsequently brought to an anaerobic reducing environment. The enzymatic reaction used ATP and oxidized coenzyme F420 as substrates and inorganic pyrophosphate was formed next to F390. GTP could be used instead of ATP resulting in a guanylylated derivative. The crude cell-free extract showed K m values of 154 μM for coenzyme F420 and 2.4 mM for ATP. A partially purified enzyme preparation exhibited a K eq of 0.32. In accordance, coenzyme F420 and ATP could be synthesized from F390 and PPi by the reverse reaction.  相似文献   

6.
Population differentiation in an annual legume: genetic architecture   总被引:10,自引:0,他引:10  
Abstract. The presence or absence of epistasis, or gene interaction, is explicitly assumed in many evolutionary models. Although many empirical studies have documented a role of epistasis in population divergence under laboratory conditions, there have been very few attempts at quantifying epistasis in the native environment where natural selection is expected to act. In addition, we have little understanding of the frequency with which epistasis contributes to the evolution of natural populations. In this study we used a quantitative genetic design to quantify the contribution of epistasis to population divergence for fitness components of a native annual legume, Chamaecrista fasciculata . The design incorporated the contrast of performance of F2 and F3 segregating progeny of 18 interpopulation crosses with the F1 and their parents. Crosses were conducted between populations from 100 m to 2000 km apart. All generations were grown for two seasons in the natural environment of one of the parents. The F1 often outperformed the parents. This F1 heterosis reveals population structure and suggests that drift is a major contributor to population differentiation. The F2 generation demonstrated that combining genes from different populations can sometimes have unexpected positive effects. However, the F3 performance indicated that combining genes from different populations decreased vigor beyond that due to the expected loss of heterozygosity. Combined with previous data, our results suggest that both selection and drift contribute to population differentiation that is based on epistatic genetic divergence. Because only the F3 consistently expressed hybrid breakdown, we conclude that the epistasis documented in our study reflects interactions among linked loci.  相似文献   

7.
Abstract Methanosphaera stadtmanae , a member of the Methanobacteriales reduces methanol, but not CO2 with H2 or 2-propanol to produce methane. In cell-free extracts of M. stadtmanae the activities of several enzymes involved in electron transfer were measured. The activities of an F420-nonreactive hydrogenase, NADP+: F420 oxidoreductase, NADP+-dependent 2-propanol dehydrogenase, and a methyl viologen dependent F420 dehydrogenase were observed. Based on the presence of these particular enzyme activities, their cofactor requirements and the absence of F420-dependent hydrogenase activity, a model of the electron transport pathway through the coenzyme F420 to provide electrons for biosynthesis, was formulated.  相似文献   

8.
Summary. Two-dimensional agarose gel (pH 8.6)-horizontal polyacrylamide gel (pH 9.0) electrophoresis of horse serum samples, followed by general protein staining, revealed genetic polymorphism of an unidentified protein tentatively designated serum protein 3 (SP3). The SP3 fractions appeared distinctly when a 14% concentration of acrylamide was used in the separation gels. The 2-D mobilities of SP3 fractions were quite similar to that of albumin. Family data were consistent with the hypothesis that the observed SP3 phenotypes were controlled by four co-dominant, autosomal alleles ( D,F,I,S ). Evidence was provided that the F allele can be further divided into two alleles ( F 1 and F 2); the mobilities of F1 and F2 variants were very similar. Each of the SP3 alleles gave rise to one fraction and each of the heterozygous types showed two fractions. More than 600 horses representing five different breeds (Swedish Trotter, North-Swedish Trotter, Thoroughbred, Arab and Polish Tarpan) were typed for SP3, and allele frequency estimates were calculated. SP3 was highly polymorphic in all breeds studied.  相似文献   

9.
Quantitative trait loci (QTL) influencing the weight of abdominal fat (AF) and of breast muscle (BM) were detected on chicken chromosome 5 (GGA5) using two successive F2 crosses between two divergently selected 'Fat' and 'Lean' INRA broiler lines. Based on these results, the aim of the present study was to identify the number, location and effects of these putative QTL by performing multitrait and multi-QTL analyses of the whole available data set. Data concerned 1186 F2 offspring produced by 10 F1 sires and 85 F1 dams. AF and BM traits were measured on F2 animals at slaughter, at 8 (first cross) or 9 (second cross) weeks of age. The F0, F1 and F2 birds were genotyped for 11 microsatellite markers evenly spaced along GGA5. Before QTL detection, phenotypes were adjusted for the fixed effects of sex, F2 design, hatching group within the design, and for body weight as a covariable. Univariate analyses confirmed the QTL segregation for AF and BM on GGA5 in male offspring, but not in female offspring. Analyses of male offspring data using multitrait and linked-QTL models led us to conclude the presence of two QTL on the distal part of GGA5, each controlling one trait. Linked QTL models were applied after correction of phenotypic values for the effects of these distal QTL. Several QTL for AF and BM were then discovered in the central region of GGA5, splitting one large QTL region for AF into several distinct QTL. Neither the 'Fat' nor the 'Lean' line appeared to be fixed for any QTL genotype. These results have important implications for prospective fine mapping studies and for the identification of underlying genes and causal mutations.  相似文献   

10.
Marek's disease (MD) is a lymphoproliferative disease caused by a member of the herpesvirus family, and the best understood genetic resistance to MD involves the chicken major histocompatibility complex (MHC) B -complex. Preliminary observations have suggested that MHC-like Rfp-Y genes might also influence the incidence of MD. This study describes the differentiation and definition of unique Rfp-Y genes in inbred lines 63 and 72, lines that possess identical B -complex genes, but that are resistant or susceptible to MD, respectively. To assess if Rfp-Y genes affect susceptibility to MD, 265 63× 72 F2 chickens were challenged with the JM strain of MD virus at 1 week of age and were evaluated for MD lesions at up to 10 weeks of age. Genotyping of the F2 chickens for Rfp-Y haplotypes was performed by restriction fragment length polymorphism analysis of genomic DNA using Taq I and a B-FIV probe. Analysis of variance and interval mapping procedures were used to determine association between the Rfp-Y haplotypes and the phenotypic MD values of the F2 chickens. The cosegregation analysis of 265 F2 chickens indicated that there was no association between Rfp-Y haplotypes and MD susceptibility. Furthermore, the fact that the Rfp-Y haplotypes fit the 1:2:1 segregation ratio and the Rfp-Y allele frequencies did not differ significantly from 0·5 in the full population or in selected subpopulations (of either 40 MD-resistant or 39 MD-susceptible chickens) also indicated that Rfp-Y haplotypes do not significantly influence MD susceptibility. We conclude that Rfp-Y haplotypes do not play a major role in determining the genetic susceptibility to MD in 63× 72 F2 White Leghorn chickens.  相似文献   

11.
Following a 2-week treatment with glyphosate [N-(phosphonomethyl)glycine] changes in peroxidase (EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.14.18.1) activities of yellow nutsedge ( Cyperus esculentus L.) plants, were determined. Glyphosate caused significant increases of both activities. Isoelectric focusing gave 3 species (F1, F2 and F3) of peroxidase activity, at pl 3.8, 4.4 and 4.8, and 4 species (Fa, Fb, Fc and Fd) of PPO activity at pl 7.0, 7.5, 7.8 and 9.5. The activity of the 4 active forms of PPO increased with increasing glyphosate dose up to 10−2 M . The effect of the herbicide on the 3 fractions with peroxidase activity was to change their relative activities. Highest F1 activity was found in control plants whereas the F2 fraction was the predominant form in the plants treated with glyphosate at 10−2 M and the highest F3 activity occurred in plants treated with 5 × 10−3 M glyphosate. The increased PPO activity could produce phytotoxic o -quinones, and variations in peroxidase isoenzymes activity could enhance isoperoxidases with lignin biosynthetic activity.  相似文献   

12.
Quantitative trait loci (QTL) for fat deposition, growth and muscling traits have been previously mapped on the basis of low-density linkage maps in a wild boar × Meishan F2 family to the chromosome X region flanked by SW2456 and SW1943 . Improved QTL resolution was possible using data for F2 animals with a marker density of 2.7 cM distance in the SW2456 to SW1943 region, including AR , SERPINA7 and ACSL4 as candidate genes. The resolution of the QTL scan was increased substantially, as evidenced by the higher F -ratio values for all QTL. Maxima of F -ratio values for fat deposition, muscling and growth traits were 28.6, 18.2 and 16.5 respectively, and those QTL positions accounted for 7.9%, 5.0% and 4.5% of the F2 phenotypic variance (VF2) respectively. QTL for fatness and growth and for most muscling traits mapped near ACSL4 , with the exception of the QTL for ham traits that mapped proximally, in the vicinity of AR . An analysis performed separately for F2 male animals showed the predominant QTL affecting fat deposition traits (up to 13.6% VF2) near AR and two QTL for muscling traits (up to 9.9% VF2) mapped close to ACSL4 . In the F2 female animals, QTL affecting muscling (up to 12.1% VF2) mapped at ACSL4 and SW2456 , and QTL for fat deposition (10% VF2) and growth (up to 10.5% VF2) mapped at ACSL4 .  相似文献   

13.
We have previously shown that seizures induce the formation of F2-isoprostanes (F2-IsoPs), one of the most reliable indices of oxidative stress in vivo . Isofurans (IsoFs) are novel products of lipid peroxidation whose formation is favored by high oxygen tensions. In contrast, high oxygen tensions suppress the formation of F2-IsoPs. The present study determined seizure-induced formation of IsoFs and its relationship with cellular oxygen levels (pO2). Status epilepticus (SE) resulted in F2-IsoP and IsoF formation, with overlapping but distinct time courses in hippocampal subregions. IsoF, but not F2-IsoP formation coincided with mitochondrial oxidative stress. SE resulted in a transient decrease in hippocampal pO2 measured by in vivo electron paramagnetic resonance oximetry suggesting an early phase of seizure-induced hypoxia. Seizure-induced F2-IsoP formation coincided with the peak hypoxia phase, whereas IsoF formation coincided with the 'reoxygenation' phase. These results demonstrate seizure-induced increase in IsoF formation and its correlation with changes in hippocampal pO2 and mitochondrial dysfunction.  相似文献   

14.
Saxifraga pentadactylis subsp. almanzorii , an endemic to the subalpine nucleus of Sierra de Gredos (central Spain), differs from its closest relative, subsp. willkommiana , by its less showy petals. An artificial crossing program was carried out in order to assess the degree of reproductive isolation between the subspecies. To facilitate interpretation of the results, the program was extended to 10 other interspecific hybrid combinations within sect. Saxifraga . All the data gathered are congruent with the occurrence of two evolutionary scenarios. Interspecific crossings, rendering moderate to high seed-set (in obtaining the F1), and vigorous but relatively sterile F1 offspring, reveal reproductive barriers at the level of the F1 fertility, probably originated as a byproduct of divergent evolution. In contrast, intraspecific crossings within S. pentadactylis resulted in seed-set values lower than expected (in obtaining the F1), in a majority of weak non-viable F1 offspring but also in a few fertile F1 hybrid specimens which were able to originate F2 offspring. This second pattern reveals reproductive barriers at the level of the F1 vitality, probably arisen in a quite abrupt fashion. The lower P/O for subsp. almanzorii as compared to subsp. willkommiana , together with the rest of the evidence suggest that the reproductive barriers between them might be the product of active selection against hybridization achieved by incrementing the levels of autogamy in the former.  相似文献   

15.
Hierarchy is the main criterion for informativeness in a data set, even if no explicit reference to evolution as a causal process is provided. Sequence data (nuclear ribosomal DNA ITS) from Armeria (Plumbaginaceae) contains a certain amount of hierarchical structure as suggested by data decisiveness and distribution of tree lengths. However, ancillary evidence suggests that extensive gene flow and biased concerted evolution in these multicopy regions have significantly shaped the ITS data set. This argument is discussed using parsimony analysis of four data sets, constructed by combining wild sequences with those from different generations of artificial hybrids (wild + F1, F2, and backcrosses; wild + backcrosses; wild + F1; wild + F2). Compared to the F1 hybrids, F2 show a certain degree of homogenization in polymorphic sites. This effect reduces topological disruption caused by F1 and is considered to be illustrative of how extensive gene flow and biased concerted evolution may have modeled the wild ITS data. The possibility that hierarchy has arisen as a result of—or despite a significant contribution from—those two such potentially perturbing forces raises the question of what kind of signal are we recovering from this molecular data set.  相似文献   

16.
The serum albumin genotypes of 65 Jersey × Hariana (F1), 75 Holstein Friesian × Hariana (F1) and 47 Brown Swiss × Hariana (F1) crossbred cows were determined by starch gel electrophoresis. Two albumin alleles AlbF and Albs , but only either as AlbF homozygotes or AlbFs heterozygotes, were observed amongst these animals. There were no AlbS homozygotes or other genotypes. Highly significant relationships between albumin genotypes and both birth weights and first-lactation milk yields of these cows were observed. The AlbF allele was associated with increased milk yield and greater birth weights.  相似文献   

17.
The evolution of F1 postzygotic incompatibilities in birds   总被引:1,自引:1,他引:0  
Abstract.— We analyzed the rate at which postzygotic incompatibilities accumulate in birds. Our purposes were to assess the role of intrinsic F1 hybrid infertility and inviability in the speciation process, and to compare rates of loss of fertility and viability between the sexes. Among our sample more than half the crosses between species in the same genus produce fertile hybrids. Complete loss of F1 hybrid fertility takes on the order of millions of years. Loss of F1 hybrid viability occurs over longer timescales than fertility: some viable hybrids have been produced between taxa that appear to have been separated for more than 55 my. There is strong support for Haldane's rule, with very few examples where the male has lower fitness than the female. However, in contrast to Drosophila , fertility of the homogametic sex in the F1 appears to be lost before viability of the heterogametic sex in the F1. We conclude that the time span of loss of intrinsic hybrid fertility and viability is often, but not always, longer than the time to speciation. Premating isolation is an important mechanism maintaining reproductive isolation in birds. In addition, other factors causing postzygotic reproductive isolation such as ecological causes of hybrid unfitness, reduced mating success of hybrids, and genetic incompatibilities in the F2s and backcrosses may often be involved in the speciation process.  相似文献   

18.
Adult roach, bream and their presumed F1 hybrid from an Anglian Water reservoir were identified on the basis of morphological and meristic characteristics. The hybrid was clearly intermediate. Four hybrid breeding crosses were induced to spawn by hypophysis. A bream × roach cross (female named first) failed to produce fertile eggs, whereas F1 hybrid × roach, roach × F1 hybrid and F1 hybrid × F1 hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F1 hybrid × roach back-cross (56%) but low for the others (<2%), in comparison to the pure species controls (roach 69%, bream 76%). Progeny from these crosses were reared until anal fin rays could be counted. These counts indicated intermediacy between the parents and back-crossed individuals, and similarity between F1 hybrids and their F2 progeny.  相似文献   

19.
Abstract: Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, γ-glutamyl transpeptidase, and prostacyclin synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F, was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F. Comparison of the synthesis of prostaglandins 6-keto-F, E2, and F showed that 6-keto-prostaglandin F was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D2 was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles of prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow.  相似文献   

20.
Abstract. Twenty cultivars of spring wheat were examined for variation in abscisic acid (ABA) accumulation following partial dehydration of excised leaves. A 3-fold range of ABA concentration was obtained.
A cross between two cultivars which differed in drought-induced ABA accumulation was used to study the heritability of ABA accumulation and to develop lines differing in their capacity to accumulate ABA. Broad sense heritability was 0–32 between the F2 and F3 generations and 0–70 between the F3 and F4 generations. Apparent homozygosity for ABA accumulation was achieved in several selections at the F4. The possible significance for drought resistance of differences in capacity to accumulate ABA is discussed.  相似文献   

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