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1.
Artificial cross combinations of tetraploid Hyla versicolor were analyzed electrophoretically using a polymorphic malate dehydrogenase locus (MDH-1) to determine the mechanism of chromosome segregation. Models for differentiating between disomic and tetrasomic inheritance are presented and tested. In some crosses progeny genotypes fit a disomic mode of segregation. In other crosses there is only evidence for a tetrasomic mode of segregation. Additional crosses produced genotypic ratios which conformed to either a disomic or tetrasomic mode of segregation. The same type of inheritance was demonstrated for any individual when used in multiple cross combinations. These results suggest that there exists in H. versicolor a polymorphism with respect to segregation of gametes, resulting from differences in chromosome pairings during meiosis I.  相似文献   

2.
Summary Segregation at one of the loci controlling tiller-base pigmentation was studied to determine the mode of inheritance in tetraploid hybrids between Lolium perenne and L. multiflorum. The results could be explained by tetrasomic inheritance and thus did not support previous reports of a degree of preferential chromosome pairing in this material. However, double reduction and aneuploidy may to some extent have masked any tendency to disomic segregation brought about by preferential pairing. Moreover, there was significant heterogeneity between families in the segregation ratios which may indicate genetically controlled differences in pairing behaviour. The results are related to previous cytological and genetic studies.  相似文献   

3.
Artificial tetraploid somatic hybrids have been developed for sterile triploid citrus breeding by sexual hybridization between diploid and tetraploid somatic hybrids. The genetic structure of diploid gametes produced by tetraploid genotypes depends on the mode of chromosome association at meiosis. In order to evaluate tetraploid inheritance in a tetraploid interspecific somatic hybrid between mandarin and lemon, we performed segregation studies using cytogenetic and single sequence repeat molecular markers. Cytogenetic analysis of meiosis in the somatic hybrid revealed 11% tetravalents and 76% bivalents. Inheritance of the tetraploid hybrid was analyzed by genotyping the triploid progeny derived from a cross between a diploid pummelo and the tetraploid somatic hybrid, in order to derive genotypes of the meiospores produced by the tetraploid. A likelihood-based approach was used to distinguish between disomic, tetrasomic, and intermediate inheritance models and to estimate the double reduction rate. In agreement with expectations based the cytogenetic data, marker segregation was largely compatible with tetrasomic and inheritance intermediate between disomic and tetrasomic, with some evidence for preferential pairing of homoeologous chromosomes. This has important implications for the design of breeding programs that involve tetraploid hybrids, and underscores the need to consider inheritance models that are intermediate between disomic and tetrasomic.  相似文献   

4.
In order to assess the potential for interspecific recombination between the cultivated Solanum tuberosum (tbr) and the sexually isolated wild species Solanum commersonii (cmm), genetic analysis of a F2 progeny obtained by selfing one tetraploid cmm (+) tbr somatic hybrid was performed through molecular markers. For this purpose, the extent of disomic and/or tetrasomic inheritance of species-specific RAPD and AFLP markers was determined by following their segregation in a 90-genotype progeny, and testing all the possible segregation ratios in a selfed tetraploid progeny. The RAPD analysis performed using 16 primers revealed that the cmm-specific RAPDs were mainly (93.7%) duplex markers and were equally distributed between loci with a disomic (46.7%) and tetrasomic (53.3%) inheritance. The AFLP analysis led to the identification of 272 (58%) informative AFLPs, which were either cmm- or tbr-specific markers. About 63% of cmm-specific AFLPs were duplex loci, most of which (92.6%) were inherited as tetrasomic loci. As regards the tbr-specific AFLPs, the percentage of simplex loci (52.9%) was higher than that of duplex loci (32.6%), and among the latter most (88.5%) were inherited as tetrasomic loci. Overall, 130 duplex markers were found, of which 53.1% were cmm-specific and 46.9% were tbr-specific. Out of 130 markers, 18 (13.8%) were inherited as disomic, and 112 (86.2%) as tetrasomic, loci. This implies that the majority of duplex markers were located on chromosomes which at meiosis tend to randomly pair as bivalents or to form tetravalents. The total number of simplex loci was 119, and most of them (82.3%) were tbr-specific loci. In some cases the observed segregation ratios even allowed us to clearly determine whether a random chromosome or chromatid segregation was detected. This was the case of three cmm-specific RAPDs, 19 cmm- and 25 tbr-specific AFLPs, which fit a 20.8:1 or 2.5:1 ratio, both cases for which a clear random chromatid segregation can be assumed, since they represent the limit of segregation expected when the distance between the locus and the centromere always leads to a cross-over event. The percentage of ascertained crossing-over events was around 37% out of the tetrasomically inherited loci clearly identified (128 loci), a value indicating that the flow of genes from the sexually isolated S. commersonii to the cultivated potato is possible, for at least a large proportion of genes. Received: 23 July 2001 / Accepted: 9 August 2001  相似文献   

5.
The mode of inheritance in tetraploid cut roses   总被引:2,自引:0,他引:2  
Tetraploid hybrid tea roses (Rosa hybrida) represent most of the commercial cultivars of cut roses and form the basis for breeding programmes. Due to intensive interspecific hybridizations, modern cut roses are complex tetraploids for which the mode of inheritance is not exactly known. The segregation patterns of molecular markers in a tetraploid mapping population of 184 genotypes, an F(1) progeny from a cross of two heterozygous parents, were investigated for disomic and tetrasomic inheritance. The possible occurrence of double reduction was studied as well. We can exclude disomic inheritance, but while our observations are more in line with a tetrasomic inheritance, we cannot exclude that there is a mixture of both inheritance modes. Two novel parental tetraploid linkage maps were constructed using markers known from literature, combined with newly generated markers. Comparison with the integrated consensus diploid map (ICM) of Spiller et al. (Theor Appl Genet 122:489-500, 2010) allowed assigning numbers to each of the linkage groups of both maps and including small linkage groups. So far, the possibility of using marker-assisted selection in breeding of tetraploid cut roses and of other species with a tetrasomic or partly tetrasomic inheritance, is still limited due to the difficulties in establishing marker-trait associations. We used these tetraploid linkage maps to determine associations between markers, two morphological traits and powdery mildew resistance. The knowledge on inheritance and marker-trait associations in tetraploid cut roses will be of direct use to cut rose breeding.  相似文献   

6.
The objective of this work was to determine the type of inheritance (disomic/polysomic) in tetraploid (2n=4x=40) Paspalum notatum and investigate the transmission pattern of the chromosome region associated with apospory. An F1 family segregating for the reproductive mode (aposporous vs non-aposporous) was generated by crossing a tetraploid sexual plant as female parent with an apomictic individual as pollen donor. Pollen mother cells from both parental plants were examined to ascertain chromosome-pairing behavior at meiosis. The high rate of quadrivalent chromosome associations indicated an autotetraploid origin of the species, although bivalent pairing and occasional univalents were detected. The observation of a lagging bivalent, a bridge of chromatin, or two aligned laggards in the aposporous parent suggested a chromosome inversion in this strain. Segregation ratios of AFLP markers and the proportion of linkages in repulsion versus coupling phase denoted tetrasomic inheritance, but markers displaying disomic ratios were also observed. Preferential chromosome pairing (disomic inheritance) in the chromosome segment related to apospory was detected. The possible relationship between a chromosome rearrangement and the inheritance of apospory is discussed.Communicated by H.C. Becker  相似文献   

7.
Gene exchanges between Solanum melongena and its allied relative Solanum aethiopicum are a crucial prerequisite for introgression of useful traits from the allied species into the cultivated eggplant. In order to evaluate the extent of genetic recombination between the 2 species, biochemical and molecular markers were employed. A dihaploid population obtained through anther culture of the corresponding tetraploid somatic hybrids was genetically analyzed. The extent of disomic/tetrasomic inheritance and segregation ratios of 3 isozyme systems and intersimple sequence repeat (ISSR) markers were evaluated. The dihaploids, being derived from microspores, allowed for simple, complete, and accurate analyses. The segregation of 280 ISSR markers (110 aethiopicum-specific, 104 melongena-specific, and 66 monomorphic) were evaluated in 71 dihaploids. According to the genetic constitution (simplex/duplex/triplex), almost 64% of the fragments revealed the tetrasomic and/or disomic inheritance. With regard to the assigned species-specific fragments, 68% and 4% were unambiguously the result of tetrasomic and disomic inheritance, respectively. Twenty-four of the 66 monomorphic ISSRs were inherited according to random chromatid segregation. The phenotypes of glucose-6-phosphate dehydrogenase (G-6-PDH), 6-phosphogluconate dehydrogenase (6-PGDH), and shikimate dehydrogenase (SKDH) were studied in 70 dihaploids and inferences were made about the allelic state of their 5 loci. The isozyme markers segregated in the dihaploids in a distorted manner, their segregations did not fit in with any of the expected segregation ratios. However, tetrasomic inheritance might be suggested for G-6-PDH 2 and SKDH 1 loci. Our results demonstrated that gene exchanges occurred readily in the somatic hybrids between S. melongena and S. aethiopicum gr. Gilo.  相似文献   

8.
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  相似文献   

9.
Marsden JE  Schwager SJ  May B 《Genetics》1987,116(2):299-311
The recently evolved autotetraploid frog, Hyla versicolor , was examined electrophoretically for evidence of genomic restructuring leading to diploidization. Loci were tested against the progeny ratios expected if inheritance was disomic vs. tetrasomic. Two loci (Mpi and Sod-2) appeared to be inherited tetrasomically, one (Mdh-2) appeared to be inherited disomically, and one (Tpi) appeared to be inherited disomically in one family and tetrasomically in another family, when tested conventionally against 1:2:1 and 1:4:1 segregation ratios. The minimum number of progeny required for this type of analysis for codominant alleles is shown to be 92. Progeny resulting from double reduction were observed, and the occurrence of a null allele class at Mpi was noted. A reexamination of expected progeny ratios in tetraploid organisms reveals that tetrasomic inheritance patterns cannot be predicted without adequate knowledge of the amount of crossing-over, the proportion of tetravalents vs. random bivalents that are formed, and the ratio and types of centromere segregation (alternate and adjacent) that occur from tetravalents in the species being studied. However, disomic inheritance can be unambiguously confirmed only by the production of all heteroallelic gametes from homobivalent, symmetrically heterozygous individuals. In addition, a method is described for estimating genecentromere distances using the ratio of progeny genotypes in certain crosses in tetraploid species.  相似文献   

10.
M. S. Olson 《Genetics》1997,147(4):1933-1942
Discrimination between disomic and tetrasomic inheritance aids in determining whether tetraploids originated by allotetraploidy or autotetraploidy, respectively. Past assessments of inheritance in tetraploids have used analyses whereby each inheritance hypothesis is tested independently. I present a Bayesian analysis that is appropriate for discriminating among several inheritance hypotheses and can be used in any case where hypotheses are defined by discrete distributions. The Bayesian approach incorporates prior knowledge of the probability of occurrence of disomic and tetrasomic hypotheses so that the results of the analysis are not biased by the fact that there is a single tetrasomic hypothesis and multiple disomic hypotheses. This analysis is used to interpret data from crosses in the tetraploid Astilbe biternata, a herbaceous plant native to the southern Appalachians. The progeny ratios from all crosses favored the hypothesis of disomic inheritance at both the PGM and slow-PGI loci. These results support earlier cytogenetic evidence for the allotetraploid origin of Astilbe biternata.  相似文献   

11.
Intra- and interspecific cross combinations between the tetraploid treefrog Hyla versicolor, and between H. versicolor and the diploid treefrog Hyla chrysoscelis were performed. Progeny phenotypes resulting from these crosses were examined electrophoretically using a polymorphic glutamate oxaloacetic transminase (GOT-1) locus, to determine the mechanism of chromosome segregation in H. versicolor, and to test theoretical expectations for isozyme expression in interspecific (2n x 4n or 4n x 2n) hybrids. In some intraspecific tetraploid crosses progeny phenotypes fit a disomic mode of segregation, whereas in other crosses a tetrasomic mode of segregation was the most probable. Additional crosses produced phenotypic ratios that conformed to either a disomic or tetrasomic mode of segregation. These results suggest that a polymorphism, with respect to segregation of gametes, exists in H. versicolor, resulting from differences in chromosome pairings during meiosis I. This polymorphism in gametic segregation occurred in both sexes. Certain crosses, however, produced phenotypic ratios that did not conform to any chromosome segregation model. Progeny phenotypes observed from most interspecific crosses conformed to expected interspecific isozyme staining intensity models. Symmetrical heterozygotes, representing either a single dose for both alternate alleles or double doses for both alternate alleles, were also observed. Such phenotypes are unexpected in triploid progeny. A null allele was postulated to account for the aberrant segregation ratios and phenotypes observed in certain intra- and interspecific crosses.  相似文献   

12.
We examined the inheritance of allelic variation at an isozyme locus, MDH-B, duplicated by ancestral polyploidy in salmonid fishes. We detected only disomic segregation in females. Segregation ratios in males were best explained by a mixture of disomic and tetrasomic inheritance. We propose a two-stage model of pairing in male meiosis in which, first, homologous chromosomes pair and recombine in the proximal region of the chromosome. Next, homeologous chromosomes pair and recombine distally. We suggest that this type of tetrasomic inheritance in which centromeres segregate disomically should be referred to as ``secondary tetrasomy' to distinguish it from tetrasomy involving entire chromosomes (i.e., ``primary tetrasomy'). Differences in segregation ratios between males indicate differences between individuals in the amount of recombination between homeologous chromosomes. We also consider the implication of these results for estimation of allele frequencies at duplicated loci in salmonid populations.  相似文献   

13.
Tetraploid inheritance has two extremes: disomic in allotetraploids and tetrasomic in autotetraploids. The possibility of mixed, or intermediate, inheritance models has generally been neglected. These could well apply to newly formed hybrids or to diploidizing (auto)tetraploids. We present a simple likelihood-based approach that is able to incorporate disomic, tetrasomic, and intermediate inheritance models and estimates the double-reduction rate. Our model shows that inheritance of microsatellite markers in natural tetraploids of Rorippa amphibia and R. sylvestris is tetrasomic, confirming their autotetraploid origin. However, in F(1) hybrids inheritance was intermediate to disomic and tetrasomic inheritance. Apparently, in meiosis, chromosomes paired preferentially with the homolog from the same parental species, but not strictly so. Detected double-reduction rates were low. We tested the general applicability of our model, using published segregation data. In two cases, an intermediate inheritance model gave a better fit to the data than the tetrasomic model advocated by the authors. The existence of inheritance intermediate to disomic and tetrasomic has important implications for linkage mapping and population genetics and hence breeding programs of tetraploids. Methods that have been developed for either disomic or tetrasomic tetraploids may not be generally applicable, particularly in systems where hybridization is common.  相似文献   

14.
Inheritance in the expression of amplicons for four microsatellite primer pairs was determined using 10 families created from gametes of wild lake sturgeon (Acipenser fulvescens). Loci Afu34 and Afu68 expressed a maximum of two even-intensity bands per individual and had progeny genotype ratios that fit disomic inheritance (P > 0.05). Some variation exhibited at Afu34 and Afu68 was attributable to a null allele. Genotype expression at both loci also indicated that one female parent had transmitted unreduced gametes. Primer Afu39 amplified products that exhibited four gene doses, where genotype counts fit expected ratios for disomic inheritance (P > 0.05) indicating amplification of products from two disomic loci that share alleles. Meiotic drive was evident at the Afu39 loci based on a test for random segregation (P < 0.05). Only the expression of Afu19 gave evidence of tetrasomic inheritance based on a single progeny potentially produced by a double reduction gamete. No evidence for proposed octoploid inheritance was observed.  相似文献   

15.
Summary Autotetraploid gene segregation was studied in Zea mays L. using a marking system of two very closely linked genes (A 1 and Sh 2) in the repulsion phase. This system makes it possible to identify many euploid and aneuploid genotypes and enables the estimation of some parameters of autotetraploid gene segregation such as double reduction, numerical nondisjunction, and the relative transmission frequencies of monosomic, disomic, and trisomic gametes. It was found that these three types of gametes did not function at the same rates on the male and female sides. Differences in observed segregation ratios between reciprocal testcrosses were explained by this phenomenon. Estimates of the frequency of double reduction were made for loci used after eliminating the effect of numerical non-disjuction on the segregation ratios. The value of double reduction appears to be the same in the male and female tetrasomic tetraploid. Tetraploids which were disomic for chromosome 3 were not isolated although they might be expected to be common in the progeny of self-fertilized or sib-crossed trisomic tetraploids. Their absence may be explained in part by the low rate of transmission of monosomic gametes from the male parent. Autotetraploid populations which are unstable for chromosome number probably achieve an equilibrium between forces which produce aneuploidy and forces which remove aneuploids from the population.This paper is dedicated to Dr. M. M. Rhoades.Cooperative investigations of the Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Agronomy Department, Missouri Agricultural Experiment Station. Journal Series No. 6557.  相似文献   

16.
Current systems of estimating gene segregation in autotetraploids usually are based on two extreme methods: chromosome segregation with absolute centromere linkage, or maximum equational segregation with crossing over always occurring between the centromeres and marker genes. The hiatus between the two methods is unacceptable quantitatively, and segregation of the d gene in tomato shows that neither method predicts an acceptable fit. We present a new meiotic configuration (MC) method of analyzing tetrasomic inheritance in autotetraploids that allows more accurate estimations of all intermediate types of segregation. The method is based on a maximum of two chiasmata per bivalent and four per quadrivalent. The theoretically expected numbers of bivalents and chain and circle quadrivalents are derived first. Chromosome frequencies from these configurations are then used to determine relative contributions from each configuration to the gamete genotypes by way of newly developed tables for gene segregation in various autotetraploid genotypes. The large sample sizes from classic 4x tomato (Solanum lycopersicum L.) data are used to demonstrate the stepwise method of calculating gamete genotypes, and the method gives acceptable fits for the data tested. The interspecific tetraploid hybrid Solanum lycopersicum × S. pimpinellifolium had good fits to expected autotetraploid segregation, supporting its autoploid nature and the fact that taxonomic rank should not be a consideration in designating categories of polyploids. Autotetraploid allozyme segregation data for several genes in one genus of another family had acceptable and usually better fits to the MC expectations than to the standard methods.  相似文献   

17.
Many eukaryotic genomes contain a large fraction of gene duplicates (or paralogs) as a result of ancient or recent whole‐genome duplications (Ohno 1970 ; Jaillon et al. 2004 ; Kellis et al. 2004 ). Identifying paralogs with NGS data is a pervasive problem in both ancient polyploids and neopolyploids. Likewise, paralogs are often treated as a nuisance that has to be detected and removed (Everett et al. 2012 ). In this issue of Molecular Ecology Resources, Waples et al. ( 2015 ) show that exclusion might not be necessary and how we may miss out on important genomic information in doing so. They present a novel statistical approach to detect paralogs based on the segregation of RAD loci in haploid offspring and test their method by constructing linkage maps with and without these duplicated loci in chum salmon, Oncorhynchus keta (Fig.  1 ). Their linkage map including the resolved paralogs shows that these are mostly located in the distal regions of several linkage groups. Particularly intriguing is their finding that these homoeologous regions appear impoverished in transposable elements (TE). Given the role that TE play in genome remodelling, it is noteworthy that these elements are of low abundance in regions showing residual tetrasomic inheritance. This raises the question whether re‐diploidization is constrained in these regions and whether they might have a role to play in salmonid speciation. This study provides an original approach to identifying duplicated loci in species with a pedigree, as well as providing a dense linkage map for chum salmon, and interesting insights into the retention of gene duplicates in an ancient polyploid.  相似文献   

18.
Summary Eight progenies from controlled crosses and one self-progeny of apple were analysed by electrophoresis for six leaf enzymes. Based on a polyploid origin for this species, three hypotheses were tested: monogenie disomic, bigenic disomic and tetrasomic inheritance. Three enzymes exhibited monogenic inheritance; two exhibited bigenic disomic inheritance specified by two homoeologous genes; and one exhibited bigenic disomic inheritance due to two linked genes. In all cases tetrasomic inheritance was disproved. These results agreed with previous data obtained from pollen isozyme analysis. They indicated a probable allopolyploid origin of the apple genome and the loss of duplicated gene expression in some cases.  相似文献   

19.
Meiotic pairing in homothallic S. cerevisiae was studied by tetrad analysis, using strains that were trisomic or tetrasomic for chromosome I. The disomic segregants of these strains produce tetrasomic spore colonies that can be distinguished by their phenotype. Results indicated the existence of preferential pairing and nonrandom assortment of chromosomes at meiosis I. The frequency of crossing over is apparently normal in at least some regions when non-preferred pairing occurs.  相似文献   

20.
Lake sturgeon (Acipenser fulvescens) are of conservation concern in North America. To facilitate the recovery of this fish species, an understanding of their population genetic structure is necessary to develop and implement spatially and temporally appropriate management actions. Until recently, few genetic data using nuclear loci have been collected, primarily due to the paucity of suitable genetic markers because most microsatellite loci in lake sturgeon appeared to be tetrasomic. The authors identified nine microsatellite loci (from 254 examined) that were putative polymorphic disomic loci and tested their conformance to a disomic mode of inheritance using three lake sturgeon families. The objectives of the study were to: (i) confirm the disomic status of the nine loci through inheritance testing, and (ii) standardize the genetic markers among participating laboratories. At all nine loci, disomic inheritance were confirmed, and all nine loci segregated independently in the 26 of 36 loci pairs possible to test. One of the nine loci showed non‐Mendelian segregation, possibly due to meiotic drive and/or selection. Three progeny had peak patterns inconsistent with disomy at one or more loci. The nine loci when combined with four microsatellite loci previously confirmed in other studies as disomic in lake sturgeon now yield a suite of 13 microsatellite markers. These 13 markers have been standardized among four other laboratories to facilitate building an inter‐laboratory genetic database for lake sturgeon.  相似文献   

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