A genetic linkage map of rye (Secale cereale L.)

 A genetic linkage map of rye composed of 91 loci (88 RFLP, two morphological and one isozyme markers) has been developed using two reciprocal crosses. The RFLP loci covering all seven chromosomes were detected by a selection of rye, wheat, barley and oat cDNA and genomic DNA probes. The level of polymorphism was dependent on the source of the clones, with a ranking of rye>wheat>barley>oat. Distorted segregations were detected in linkage groups of chromosomes 1R, 4R, 5R and 7R. When the recombination of the two reciprocal crosses was compared, no systematic increase or decrease in one or the other direction was observed suggesting that a combination of populations of reciprocal crosses is possible. Received: 5 August 1997/Accepted: 2 September 1997     

Similarity landscapes: A way to detect many structural and sequence motifs in both introns and exons

When investigators undertake searches of DNA databases, they normally discard large numbers of alignments that demonstrate very weak resemblances to each other, retaining only those that show statistically significant levels of resemblance. We show here that a great deal of information can be extracted from these weak alignments by examining them en masse. This is done by building three-dimensional similarity landscapes from the alignments, landscapes that reveal whether an unusual number of individually nonsignificant alignments tend to match up to a particular region of the query sequence being searched. The power of the search is increased by the use of libraries consisting entirely of introns or of exons. We show that (1) similarity landscapes with a variety of features can be generated from both intron and exon libraries, using introns or exons as query sequences; (2) the landscape features are real and not a statistical artifact; (3) well-known protein motifs used as query sequences can generate various landscape features; and (4) there is some evidence for resemblances between short regions of sequence carried by introns and exons. One possible interpretation of these results is that both introns and exons may have been built up during their evolution from short regions of sequence that as a result are now widely distributed throughout eukaryotic genomes. Such an interpretation would imply that these short regions have common ancestry. Alternatively, the wide sharing of short pieces of DNA may reflect regions with particular structural properties that have arisen through convergent evolution. The similarity-landscape approach can be used to detect such widespread structural motifs and sequence motifs in the genome that might be missed by less-global searches. It can also be used in conjunction with algorithms developed for detecting significant multiple alignments by isolating promising subsets of the databases that can be examined in more detail.Correspondence to: C. Wills     

Analysis of cytoplasmic and maternal effects I. A genetic model for diploid plant seeds and animals

A genetic model for modified diallel crosses is proposed for estimating variance and covariance components of cytoplasmic, maternal additive and dominance effects, as well as direct additive and dominance effects. Monte Carlo simulations were conducted to compare the efficiencies of minimum norm quadratic unbiased estimation (MINQUE) methods. For both balanced and unbalanced mating designs, MINQUE (0/1), which has 0 for all the prior covariances and 1 for all the prior variances, has similar efficiency to MINQUE(), which has parameter values for the prior values. Unbiased estimates of variance and covariance components and their sampling variances could be obtained with MINQUE(0/1) and jackknifing. A t-test following jackknifing is applicable to test hypotheses for zero variance and covariance components. The genetic model is robust for estimating variance and covariance components under several situations of no specific effects. A MINQUE(0/1) procedure is suggested for unbiased estimation of covariance components between two traits with equal design matrices. Methods of unbiased prediction for random genetic effects are discussed. A linear unbiased prediction (LUP) method is shown to be efficient for the genetic model. An example is given for a demonstration of estimating variance and covariance components and predicting genetic effects.     

Abortion and determination of stages for embryo rescue in crosses between sweet-potato,Ipomoea batatas Lam. (2n=6x=90) and its wild relative,I. trifida (H. B. K.) G. Don. (2n=2x=30)

Summary The frequency of aborted fruits and the changes and abnormalities that occur during the embryo development in intraspecific crosses of sweet-potato Ipomoea batatas (2n=6x=90) and interspecific crosses between I. batatas and I. trifida (2n=2x=30) were investigated in order to study the causes of the low seed production. Three genotypes of I. batatas and 18 genotypes of I. trifida were intermated. The frequency of aborted fruits was below 25% in the intraspecific crosses and over 90% in the interspecific crosses. Paraffin sections were used to examine the developmental stages of fruits and seeds. Embryos in different developmental stages were observed to determine the stage of abortion. These observations permitted the identification of developmental stages of embryo rescue in interspecific crosses. There were no significant differences in the frequency of embryo abortion before the early globular stage among female sweet-potato progenitors for the intraspecific and interspecific crosses. The frequency of the late occurrence of embryo abortion (when embryo abortion occurs after the pre-globular stage) was higher in interspecific crosses (19.1%) than in intraspecific crosses (5.5%). The frequency of the late occurrence of embryo abortion in interspecific crosses was higher at the globular stage (9.6%) than at the heart stage (4.3%). Providing that embryo rescue is conducted in interspecific crosses, the estimated number of potentially viable embryos could be increased: 30 times with embryos at the globular stage; 20 times with embryos at the heart stage; and 11 times if embryos at the torpedo stage were used for the rescue with respect to the seed set. The results suggested that the appropriate time for embryo rescue in interspecific crosses is at the globular stage. If embryos could be rescued at the globular stage, it would be possible to increase the number of surviving embryos up to 30 times in interspecific crosses and 0.02 times in intraspecific crosses with respect to natural conditions without embryo rescue.This research was initiated during sabbatical of M.I. at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan     

Genetic bases for protein polymorphism in Fundulus heteroclitus (L.). I. Lactate dehydrogenase (Ldh-B), malate dehydrogenase (Mdh-A), glucosephosphate isomerase (Gpi-B), and phosphoglucomutase (Pgm-A)

Electrophoretic analysis has shown populations of F. heteroclitus to possess variants at four enzyme-coding loci: Ldh-B, Mdh-A, Gpi-B, and Pgm-A. Based on the phenotypic distribution in the F₁ generation, each variant segregates as an autosomally inherited codominant allele. A pairwise comparison of the expected phenotypic classes among these loci showed no evidence of strong linkage; however, weak linkage could not be ruled out. Despite the considerable genetic divergence of populations from the geographical extremes of this species, offspring resulting from crosses between individuals from these localities show viabilities similar to those found for crosses of local populations.This work was supported by NSF Grants GB 37548 and DEB 76-19877 and by grant from the National Geographic Society. A. R. P. is an NIH trainee supported by a training grant (No. HD00139) to the Deartment of Biology.This is contribution No. 959 of the Department of Biology, Johns Hopkins University.     

近缘单交种对协调玉米制种花期效果的研究

利用１９个黄早四改良系与单交种西农１１号的亲本之一的西黄改组成近缘单交种作母本与西农１１号的另一亲本ＷＮ１１配成三交种,以研究近缘单交种对协调玉米制种花期的效果。结果表明：近缘单交种的吐丝期均比西黄改吐丝期提前,并能与ＷＮ１１散粉期相遇;用近缘单交种配制的有些三交种产量高于或与原单交种相当,且主要农艺性状较为整齐。     

籼粳交新种质康丰A对稻瘟病抗性的遗传

康丰A是利用带有广亲和基因的籼粳亚种间杂交育成恢复系97gk419与恢复系明恢70杂交(恢复系×恢复系),所形成的胞质正常、雄性可育,而无恢复性的特殊变异新种质,再与野败胞质不育系连续回交转育成的具有特殊核遗传背景的新型水稻三系不育系。本研究通过接种不同地区的53个稻瘟病菌系,发现康丰A对华南稻区尤其是福建稻区的稻瘟病菌系具有广谱抗性。以康丰A(同型保持系康丰B)与普感品种丽江新团黑谷(LTH)杂交,获得杂交F1和F2,分别接种稻瘟病菌系81278、Guy11、FJ2009-66和98013A。接种鉴定和遗传分析表明,康丰A对4个菌系的抗性均由1对显性抗病基因控制。等位性测定表明,康丰A抗菌系81278的基因与已知抗病基因Pi-1、Pi-2、Pi-ta和Pi-3呈非等位关系,与Pi-ta(Pi-?)呈现连锁遗传,暂命名为Pi-kf1(t)。     

Retention of D genome chromosomes in pentaploid wheat crosses

The transfer of genes between Triticum aestivum (hexaploid bread wheat) and T. turgidum (tetraploid durum wheat) holds considerable potential for genetic improvement of both these closely related species. Five different T. aestivum/T. turgidum ssp. durum crosses were investigated using Diversity Arrays Technology (DArT) markers to determine the inheritance of parental A, B and D genome material in subsequent generations derived from these crosses. The proportions of A, B and D chromosomal segments inherited from the hexaploid parent were found to vary significantly among individual crosses. F(2) populations retained widely varying quantities of D genome material, ranging from 99% to none. The relative inheritance of bread wheat and durum alleles in the A and B genomes of derived lines also varied among the crosses. Within any one cross, progeny without D chromosomes in general had significantly more A and B genome durum alleles than lines retaining D chromosomes. The ability to select for and manipulate this non-random segregation in bread wheat/durum crosses will assist in efficient backcrossing of selected characters into the recurrent durum or hexaploid genotype of choice. This study illustrates the utility of DArT markers in the study of inter-specific crosses to commercial crop species.     

Mapping Quantitative Trait Loci onto a Phylogenetic Tree

Despite advances in genetic mapping of quantitative traits and in phylogenetic comparative approaches, these two perspectives are rarely combined. The joint consideration of multiple crosses among related taxa (whether species or strains) not only allows more precise mapping of the genetic loci (called quantitative trait loci, QTL) that contribute to important quantitative traits, but also offers the opportunity to identify the origin of a QTL allele on the phylogenetic tree that relates the taxa. We describe a formal method for combining multiple crosses to infer the location of a QTL on a tree. We further discuss experimental design issues for such endeavors, such as how many crosses are required and which sets of crosses are best. Finally, we explore the method's performance in computer simulations, and we illustrate its use through application to a set of four mouse intercrosses among five inbred strains, with data on HDL cholesterol.