摘要:

Recent progress in the genetic analysis of inbreeding depression in plants is reviewed. While the debate over the importance of genes of dominance versus overdominance effect continues, the scope of inferences has widened and now includes such facets as the interactions between genes, the relative abundance of major versus minor genes, life cycle stage expression, and mutation rates. The types of inferences are classified into the genomic, where many genes are characterized as an average, and the genic, where individual genes are characterized. Genomic inferences can be based upon natural levels of inbreeding depression, purging experiments, the comparison of individuals of differingF(e.g., prior inbreeding), and various crossing designs. Genic inferences mainly involve mapping and characterizing loci with genetic markers, involving either a single cross or, ideally, several crosses. Alternative statistical models for analyzing polymorphic loci causing inbreeding depression should be a fruitful problem for geneticists to pursue.Key words: inbreeding depression, genetic load, self-fertilization, QTL mapping.

ISSN:0831-2796    

DOI:10.1139/g96-001

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Based on DNA sequence analysis of 5 clones of repetitive DNA from alfalfa (Medicago sativa), we propose the existence of a dispersed middle repetitive element about 3400 bp long with a copy number in the range of 2–3 × 103per haploid genome. The average A + T content of the sequences was 54.6%, compared with 61.4% for the alfalfa genome. Sequence homologies between overlapping regions of the clones ranged from 85 to 89.5% with an average of 86.6%; sequence divergence was due largely to single base pair changes, with deletions or insertions occurring randomly across sequences. An open reading frame (ORF) in one clone, RPE15, contained homologies to cereal prolamin genes and a legumin box was located upstream of the coding region. A Northern blot of RNA from various alfalfa tissues, probed with the above clone containing this ORF, showed an extensive heterodispersed pattern of hybridization in the late stages of flower bud development but in no other tissues.Key words: lucerne,Medicago sativa, repetitive DNA, plant genomes.

ISSN:0831-2796    

DOI:10.1139/g96-002

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Random amplified polymorphic DNA (RAPD) markers were used to assess intraspecific variability and relationships in aerial yam (Dioscorea bulbiferaL.). A total of 23 accessions from different geographic locations in Africa, Asia, and Polynesia were analyzed by 10 arbitrarily chosen GC-rich decamer primers. Using cesium chloride purified genomic template DNA, highly reproducible polymorphic fingerprints were generated by all 10 primers, resulting in a total of 375 informative characters. Only eight bands were monomorphic among all investigated accessions. A binary character matrix was generated by scoring for presence/absence of a band at a particular position, transformed into a matrix of pairwise distances using either the Jaccard or a simple matching coefficient, and analyzed by neighbour joining, UPGMA (unweighted pair group method with arithmetic averaging) cluster analysis, or split decomposition. All methods of data evaluation resulted in similar groupings that reflected the geographical origin of the samples. The African accessions formed a distinct isolated group, whereas Asian and Polynesian accessions proved to be more heterogeneous. With two exceptions (var.suaviorand var.sativa), the RAPD data supported previous varietal classification based on morphological characters. Stepwise reduction of the number of evaluated characters did not affect branching patterns of the trees above a minimum threshold of 150.Key words:Dioscorea bulbifera, random amplified polymorphic DNA (RAPD), genetic variation, genetic relatedness.

ISSN:0831-2796    

DOI:10.1139/g96-003

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Two randomly amplified polymorphic DNA (RAPD) markers, OPF62700and OPH182400, tightly linked toPi-10, a dominant blast-resistance gene conferring complete resistance to isolate 106 (international race IB46) of the blast fungus were identified. To derive sequence characterized amplified regions (SCARs) from OPF62700and OPH182400, these amplified RAPD products were cloned and sequenced. Nucleotide sequence information, obtained for each end of the two linked RAPD markers, was used to design 24-mer oligonucleotide primers for PCR amplification of the respective SCARs. Polymorphisms appearing as differences in the length of the SCAR's alternate alleles were considered for the indirect selection ofPi-10. Such polymorphisms converted the linked dominant RAPD loci into codominant SCAR markers and also facilitated the indirect scoring of the blast-resistant and blast-susceptible genotypes. The development of length variant codominant SCAR markers linked to a major gene for blast resistance in rice is described. The codominant SCARs will facilitate marker-assisted selection of thePi-10locus in rice breeding programs and will also be useful as genetic markers for high resolution mapping of thePi-10region.Key words: SCAR,Pyricularia grisea,Oryza sativaL., blast resistance, indirect selection.

ISSN:0831-2796    

DOI:10.1139/g96-004

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A highly repeated DNA sequence composed of closely related subunits that ranged from 171 to 176 base pairs has been cloned and characterized in the king vulture (Sarcoramphus papa). Related sequences were also isolated in the black vulture (Coragyps atratus). This new family of avian repetitive DNA elements is here termed the "HaeIII family." Genomic DNAs from a number of avian species were probed with one of the king vulture restriction fragments. In the cathartids, the hybridization patterns showed no individual or sexual variations. A strongHaeIII ladder was present in the two aforementioned species as well as in the Andean condor (Vultur gryphus), but in the black vulture the bands of the ladder alternated in intensity. Weaker hybridization signals were obtained in two ciconids, the jabiru stork (Jabiru mycteria) and the white stork (Ciconia ciconia). TheHaeIII repeat was not detected in accipitrid birds of prey, a Polyborinae falconid, pelecanids, and psittacids.Key words: satellite DNA, New World vulture, tandem repeat,Sarcoramphus papa,Coragyps atratus.

ISSN:0831-2796    

DOI:10.1139/g96-005

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

This study was conducted to ascertain the chromosomal location and magnitude of effect of quantitative trait loci (QTL) associated with the chemical and sensory properties of sweet corn (Zea maysL.) eating quality. Eighty-eight RFLPs, 3 cloned genes (sh1,sh2, anddhn1), and 2 morphological markers (a2andse1) distributed throughout the sweet corn genome were scored in 214 F2:3families derived from a cross between the inbreds W6786su1Se1and IL731Asu1se1. Kernel properties associated with eating quality (kernel tenderness and starch, phytoglycogen, sucrose, and dimethyl sulfide concentrations) were quantified on F2:3sib-pollinated ears harvested at 20 days after pollination. Sensory evaluation was conducted on a subset of 103 F2:3families to determine intensity of attributes associated with sweet corn eating quality (corn aroma, grassy aroma, sweetness, starchiness, grassy flavor, crispness, tenderness, and juiciness) and overall liking. Single factor analysis of variance revealed significant QTL for all these traits, which accounted for from 3 to 42% of the total phenotypic variation. A proportion of the RFLP markers associated with human sensory response were also found to be associated with kernel characteristics. To our knowledge this is the first report of the identification of QTL associated with human flavor preferences in any food crop.Key words: sweet corn, RFLP, quantitative trait loci, eating quality, sensory evaluation.

ISSN:0831-2796    

DOI:10.1139/g96-006

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The Bt-10 bunt gene confers resistance to most races of the common bunt fungi,Tilletia triticiandT.laevis. The RAPD technique, employing a total of 965 decamer primers, was used to identify polymorphic markers between resistant (BW553) and susceptible ('Neepawa') near-isogenic lines. Primer 196 (5′ CTC CTC CCC C 3′) produced a 590 base pair (bp) reproducible fragment only in the resistant near-isogenic line. The 590-bp DNA fragment was present in all the 22 wheat cultivars known to carry the Bt-10 resistance gene and also in 15 resistant F2lines obtained from a cross between the resistant parent, BW553, and the susceptible parent, 'Neepawa'. The 590-bp fragment was absent in 16 susceptible cultivars tested and in 15 susceptible F2lines obtained from the cross described above. These results suggest a close linkage between the presence of the 590-bp fragment and the Bt-10 resistance gene. Primer 372 (5′ CCC ACT GAC G 3′) amplified a 1.0-kilobase (kb) fragment that was present only in the susceptible near-isogenic line. This 1.0-kb fragment was present in 13 of the 16 susceptible cultivars and in 13 of the 15 susceptible F2lines. However, the primer also amplified the 1.0-kb fragment in some resistant cultivars and resistant F2lines, suggesting a looser linkage between the occurrence of the fragment and the susceptible allele.Key words: RAPD, primer, Bt-10 bunt resistance gene, wheat, marker.

ISSN:0831-2796    

DOI:10.1139/g96-007

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Related wheat (Triticum aestivumL.) breeding lines, PI 561033, REA 9232, REA 9257, and CI 13113 were analyzed cytogenetically to characterize the association of resistance to cephalosporium stripe (caused byCephalosporium gramineumNis. & Ika.) withAgropyron elongatumchromatin. One pair ofA.elongatumchromosomes was detected in PI 561033, REA 9232, and CI 13113 by genomic in situ hybridization. The sib line of PI 561033 and REA 9232, REA 9257, which is not resistant to this disease, lacked this pair ofA.elongatumchromosomes. PI 561033 was characterized as a disomicT.aestivum–A.elongatum6Ae#2(6A) chromosome substitution line using test crosses and C-banding. In situ hybridization and test crosses showed that the donor parent, CI 13113, also had chromosome 6A substituted byA.elongatumchromosome 6Ae#2. The C-banding pattern of 6Ae#2 showed two subterminal bands on the long arm and one small band proximal to the centromere on the short arm. Based on chromosome pairing and compensation, chromosome 6Ae#2 shows a close homoeologous relationship with wheat chromosome 6A.Key words:Cephalosporium gramineum,Agropyron elongatum, in situ hybridization, C-banding, chromosome substitution.

ISSN:0831-2796    

DOI:10.1139/g96-008

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

As a first step to mapping quantitative trait loci for mating system differences, a genetic linkage map was generated from an interspecific backcross betweenMimulus guttatusandMimulus platycalyx. The linkage map consists of 99 RAPD and two isozyme markers. Eighty-one of these markers were mapped to 15 linkage groups, spanning 1437 contiguous centiMorgans, and covering 58% of the estimated genome. The genome length ofMimulusis estimated at 2474 ± 35 cM; bootstrapping indicates that only ca. 40 markers are needed to give an accurate estimate of genome length. Further statistical analyses indicate that many RAPD markers cannot be ordered with certainty and that uncertain linkage groups tend to map nonlinearly even under commonly used mapping functions. Strategies for speeding up the mapping process for a wild species and possible applications of a partial linkage map in evolutionary studies are discussed.Key words: linkage map, mating system,Mimulus, RAPD.

ISSN:0831-2796    

DOI:10.1139/g96-009

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Alien cytoplasms produce a variety of phenotypes in durum wheat (Triticum turgidum) and common wheat (Triticum aestivum) cultivars, which indicate the prevalence of cytoplasmic variability in the subtribe Triticinae. Intraspecific cytoplasmic differences have been demonstrated between the subspecies ofTriticum speltoides,Triticum dichasians, andTriticum comosum. In this study, durum wheat lines with cytoplasm from two accessions, B and C, ofTriticum longissimumwere compared, and meiotic chromosome pairing between the group 4 homoeologues from the same two accessions was examined in common wheat. First, monosomic addition or monosomic substitution lines of common wheat with cytoplasm and one chromosome (designated B) from accession B were crossed with those having cytoplasm and a chromosome designated C-1 or C-2 from accession C. In each substitution line, an alien chromosome substituted for a group 4 homoeologue. Each alien chromosome had a "selfish" (Sf) gene, which remained fixed in the wheat nucleus. The F1s had greatly reduced meiotic pairing between chromosomes B and C-1 and B and C-2, which indicated greatly reduced homology between the group 4 homoeologues from the two accessions. Second, by usingTriticum timopheeviias a bridging species, chromosome B in a common wheat line was eliminated and an euploid durum line with cytoplasm from accession B was obtained. This line was fertile. In contrast, a similarly produced durum line with cytoplasm from accession C was male sterile and retained a species cytoplasm specific (scs) nuclear gene fromT.timopheevii. In conclusion, nuclear and cytoplasmic heterogeneity pre-existed between accessions B and C and they represent varieties or incipient subspecies inT.longissimum. Alternatively, theSfgenes produced chromosomal heterogeneity and mutated cytoplasmic genes from one or both accessions.Key words: meiotic drive, selfish gene (Sf), gametocidal gene (Gc),Triticum,Aegilops.

ISSN:0831-2796    

DOI:10.1139/g96-010

出版商:NRC Research Press    

年代:1996

数据来源: NRC