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The somatic chromosomes ofTriticum turgicum var.durum cv. Langdon andT. dicoccoides (AABB tetraploids),T. timopheevii, andT. araraticum (AAGG tetraploids) were assayed for distribution patterns of a highly repeated 120bp DNA sequence by in situ hybridization. The repeated sequence appears to be an ancient sequence shared withSecale andAegilops. The distribution patterns of the chromosomes were compared to the patterns of the A and B genome chromosomes ofT. aestivum cv. Chinese Spring (AABBDD hexaploid).T. turgidum andT. dicoccoides were observed to have identical in situ hybridization patterns. In both species, nine chromosomes with a total of 21 sites of hybridization were observed. The pattern, with few exceptions, was identical to that of Chinese Spring.T. araraticum andT. timopheevii were observed to have different patterns. InT. araraticum, six chromosomes with 21 total hybridization sites are present while inT. timopheevii nine chromosomes with 19 total sites exist. Major differences in hybridization patterns were observed between the B and G genomes. The divergence of the tetraploid wheats in this study appears to have resulted in changes in location, not in amount, of the ancient repeated sequence.

Endosperm development and embryo lethality were studied in hybrids of different accessions of Aegilops squarrosa (female) and the diploid wheats Triticum boeoticum, T. monococcum and T. urartu. No cross produced plump viable seed and crosses varied with respect to both endosperm development and embryo viability. Ae. squarrosa X T. urartu hybrids showed good seed development but embryos were semi-lethal and seedling death resulted. Ae. squarrosa X T. monococcum hybrids showed endosperm abortion and embryos were lethal or semi-lethal. Ae. squarrosa X T. boeoticum hybrid seeds were dead by day 14. However, viable F1squarrosa X boeoticum hybrid plants were obtained by embryo culture at day 10 of seed development. The nature of endosperm abortion was investigated by following early endosperm development and storage-protein synthesis.

The majority of DNA that is found in most of the flowering plants appears to be non-coding DNA. Much of this excess DNA consists of nucleotide sequences which exist as multiple copies throughout the genome and are designated as repetitive sequences. Those sequences which are found in moderately high to high numbers of copies are observed to be of the greatest value as cytological markers. Moderately high copies may exist as sequences which are dispersed throughout the chromosomes of some species and not dispersed in other more distantly related species. By taking advantage of this characteristic and the technique of in situ hybridization with biotinylated probes, breakpoints of chromosomal translocations may be observed between species such as wheat and rye. Many of the high copy number repetitive sequences are organized in a tandem fashion in specific loci in the chromosome. Chromosomal identification may be accomplished by using the in situ hybridization technique. Upon in situ hybridization with a repetitive sequence isolated from Aegilops squarrosa, the patterns of the sites of hybridization allowed the D-genome chromosomes to be identified. The sequence was also observed only on the D-genome chromosomes of several polyploid species indicating its usefulness as a genome specific marker. Using this genome specificity, assessment of the orientation of the D-genome chromosomal segments ofhexaploid wheat carrying the sequence during interphase and prophase of mitotic root tip cells was possible. Repetitive DNA sequences, therefore, provide cytological markers necessary for studies of chromosomal identification, genome allocation, and genome orientation. The use of biotin-labeled DNA probes allows the technique of in situ hybridization to be performed much more rapidly and with a greater degree of safety and reliability. IN THE EARLY 1960's, studies were underway in which the DNA duplex of various organisms was disassociated into two strands and then restored by incubation under proper conditions. Before these studies were undertaken in higher organisms, the speculation was that the large dilution ofnucleotides in the vast amounts of DNA per cell would require restoration (renaturation) to proceed for months. However, certain classes ofDNA which rapidly renatured were observed in eukaryotic organisms (Britten and Kohne, 1968). These classes of DNA represent sequences which are reiterated throughout the genome and are designated as repeated DNA sequences. The most highly repeated DNA sequences may consist of simple sequence or satellite DNA. Satellite DNA is defined as DNA which can be separated from the bulk of the main DNA by ultracentrifiguation in a neutral cesium chloride density gradient. 'Received for publication 29 June 1986; revision accepted 24 November 1986. 2 Current address is Department of Agronomy, Oklahoma State University, Stillwater, OK 74078. In addition, species containing cryptic or hidden satellite sequences have been observed (Comeo, Ginelli and Polli 1970; Bendich and Anderson, 1974; Peacock et al., 1981). These cryptic sequences require changes in the conditions of centrifugation, yet still represent highly repeated DNA sequences. Triticum aestivum L. has been reported to have a 2C DNA content of approximately 34.6 picogranis (pg) (Bennett, Smith and HeslopHarrison, 1982). A genome size of this magnitude would require less than 1% of the total DNA to carry out coding and other sequencerelated functions (Flavell, 1980). Much of the excess DNA appears to be composed of repeated DNA sequences. Estimates of the amount of repeated DNA sequences in plants have ranged from 35% to 95% (Flavell et al., 1974; Murray et al., 1979; Nagl et al., 1983). In T. aestivum, the proportion of repeated DNA sequences has been estimated at 83% and has been speculated to be much higher (Flavell et al., 1974; Flavell, 1980). Repeated sequences in plants appear to be undergoing constant amplification, deletion, and sequence divergence

The chromosomes of polyploid Triticum species and the putative donor diploid species were analyzed by in situ hybridization with a repeated DNA sequence clone pSc 119 isolated from rye and also found in wheat. In Triticum aestivum cv. Chinese Spring, chromosome 4A showed one terminal site in the short arm and one terminal and two interstitial sites of hybridization in the long arm. Triticum turgidum contained a 4A chromosome identical to 'Chinese Spring' with respect to hybridization sites. Chromosome 4A of the timopheevi wheats differed from 4A of 'Chinese Spring' in that the site of the sequence on the short arm was subterminal rather than terminal. Of the A-, B-, and D-genome progenitor species, only potential B-genome donors Aegilops speltoides and Aegilops sharonensis each showed a chromosome with hybridization sites similar to 4A. This suggested that 4A belongs to the B genome. Moreover, with regard to this sequence, chromosome 4A has undergone only minor changes during the evolution of the polyploid wheats.Key words: wheat evolution, in situ hybridization, biotin labeling.

The chromosome of three tetraploid Aegilops L. species containing the D-genome were analyzed by in situ hybridization with a repeated DNA sequence clone pAS1 isolated from Aegilops squarrosa and observed to be D-genome specific. This sequence is found on all seven D-genome chromosome pairs of A. squarrosa and hexaploid wheat. Two distinct D-genome patterns were observed in the tetraploid species. The D-genome of A. cylindrica was similar to hexaploid wheat. Seven pairs of chromosomes having large amounts and numerous sites of the sequence were observed. Five chromosome pairs with fewer and smaller sites of the repetitive sequence were observed in the D-genomes of A. crassa and A. ventricosa. In addition to these major repeated sequence differences, chromosomal modifications appear to have occurred between T. aestivum and A. cylindrica and between A. crassa and A. ventricosa resulting in changes with respect to location of the sequence between the respective species. D-genome divergence with respect to pAS1 sequence appears to have occurred at least in two forms, one characterized by the changes in amount of repetitive sequence and the second by changes in location of the sequence.

Embryo age and composition of nutrient medium affected plant growth and response to vernalization in winter wheat (Triticum aestivum L.). Root and shoot development was more in older than in younger excised embryos, and more in a medium without kinetin than in one with kinetin. Kinetin (2 mg/l) in the medium did not accelerate vernalization, probably because it tended to inhibit seedling and plant growth.

Primary trisomics of the tomato spawn an array of other primary trisomics as well as such modified types as secondary, tertiary, and telo-trisomics and primary tetrasomics. Five useful, previously undescribed trisomic types were thereby obtained. Although the frequency of deviant types is very low, they can be readily screened from the total population by their markedly differing phenotypes. It is therefore feasible to obtain specific desired types of aneuploids by systematically seeking them in progenies of the corresponding primary trisomic. The data suggest, although they are not sufficiently extensive to prove, that the deviating aneuploids tend to have shorter chromosomes of the tomato complement as their extra elements and tend to be more frequent in the progeny of trisomics for the shorter chromosomes. Cytological studies of triplo-5, the most prolific source of deviants, revealed a substantial frequency of laggards and chromosomes otherwise behaving abnormally at anaphase of both meiotic divisions, thus suggesting mechanisms to account for the origin of the deviant aneuploids.

Introduction The 21 illonosomic strains of the hard red spring wheat variety, Chinese Spring (Sears 1954), have been used to develop similar strains in other varieties. The monosomic condition is transferred to a variety by initial crosses between each of the 2 1 Chinese S ~ r i n e illonosomics and the reci~ient varietv. followed L U I J ' by a series of baclccrosses to recover the genotype of the recipient variety. In developing and maintaining monosomic strains, specific chromosomes are transmitted as univalents through successive generations. Since only a few chromosomes are ltnown to ~ r o d u c e ~ h e n o t v ~ i c effects in the monosomic state. infor1 I J 1 illation concerning chromosome morphology in different varieties is needed in ~. . . identifying monoson~ics. Sasalti et nl. (1963) have presented the lengths and characteristics of inetaphase I monosomes in the hard red winter variety, Cheyenne. Similar inforhation will be reported in this paper for another winter 6ariety, Wichita, using observations at metaphase I and anaphase 11. Throughout this study emphasis was placed on factors involved in sampling and measurement which might contribute to variations in chromoson~e length. Materials and Methods The inonosomic strains for the 21 different chromoso~nes of the hard red winter variety, Wichita C.I. 11952, were used in the present study. These strains had been derived by crossing Wichita as the male parent with each of the 21 inonosomic strains of Chinese Spring developed by Dr. E. R. Sears. Repeated baclccrossing of the derived monosomic plants to Wichita followed. At the time of this study five or six bacltcrosses had been con~pleted for all the chromosomes except 3B and jD, which had been bacltcrossed twice. Seeds of the monosomic strains were planted in 7-inch pots of soil in November, 1960, and the plants were grown in a plastic greenhouse. Artificial lights were provided during the flowering period. Following a vernalization period, the day temperature was controlled at 65" to 75°F. when the outside temperature was lower, and the night temperature at 50" to 55°F. Ample water and fertilizer were applied. Based on the findings of Sasalti et nl. (1963), a satisfactory method of sampling for statistical efficiency was found to include two monosomic plants for each chron~osome, four heads per plant, two slides per head, and two measurements per slide. In order to separate the date-of-sampling effects from head effects, an effort was made to collect saillples on two different dates from the same plant. taltine two heads on each date. I ' U Thus, for each sampling period, the aim was to obtain 16 measurements for each lcind of monosome, or a total of 336 measurements for the 21 monosonles. This was most nearly achieved for the metaphase I stage at the first

Genomic DNA from six euplasmic wheat-barley addition lines and from the wheat and barley parents were analyzed for the presence of alpha-amylase gene sequences, using plasmid DNAs from two different alpha-amylase cDNA clones as hybridization probes. Barley-specific alpha-amylase gene sequences were detected only in addition lines 1 and 6 carrying barley chromosomes 1 and 6, respectively. One cDNA clone probe hybridized strongly to sequences on chromosome 6 but not to those on chromosome 1. The other cDNA clone probe preferentially hybridized to sequences on chromosome 1. It is concluded that structural genes for alpha-amylases are located on barley chromosomes 1 and 6. alpha-Amylase genes on the same chromosome appear to be closely related to one another but substantially different from those on the other chromosome.

The chromosomes of rye have been individually identified by their distinctive heterochromatin pattern with Giemsa staining and classified on the basis of their homoeology with wheat chromosomes. The constitutive heterochromatin detected by C-banding has been shown to be identical with the classical heterochromatin as seen in the pachytene of meiosis in rye.

The Feulgen procedure was applied to chromosome preparations of leaf meristems from growing plants of wheat, barley, and wheat-wheatgrass hybrids. Leaf primordia from the base of secondary tillers were pretreated in cold water (overnight, 2 C), fixed in glacial acetic acid (20 min, 2 C), hydrolyzed in 1 N HCl (14 min), stained in leuco-basic fuchsin (about 15 min) and squashed in 1% acetocarmine. The chromosome spreads from leaf meristems were generally superior to those of the root meristems of the same plant. Mitotic index in leaf meristems was higher than in root meristems in some species. The method appears useful for counting the chromosome number of growing plants, detecting chimeras, and verifying root tip chromosome counts.

The ability of immature embryos of wheat (Triticum aestivum L.) to respond to tissue culture has been shown to involve the group 2 chromosomes. The available group 2 ditelosomic and nullisomic-tetrasomic lines of ‘Chinese Spring’ wheat were used to determine the chromosome arm location and chromosome dosage effect associated with the expression of tissue culture response (TCR). Significant differences were found between the aneuploid lines and the euploid control for the expression of both regenerable callus formation and callus growth rate. A model is proposed suggesting that a major TCR gene is located on 2DL and that 2AL and 2BS possess minor TCR genes. Furthermore, a major regulatory gene controlling the expression of TCR genes may be located on chromosome 2BL.

Intergeneric hybrids of Triticum aestivum (2n=42,AABBDD) with Agropyron ciliare (2n= 28,SSYY), A. trachycaulum (2n=28,SSHH), A. yezoense (2n=28,SSYY) and A. scirpeum (2n=28) are reported for the first time. F1 hybrids of T. aestivum were also produced with A. intermedium (2n=42,E1E1E2E2Z1Z1) and A. junceum (2n=14,JuJu). All wheat-Agropyron hybrids were obtained by embryo rescue technique. Cultivars and reciprocal crosses differed for seed set, seed development and F1 plant production. The F1 hybrids were sterile. Attempts to obtain amphiploids were unsuccessful. However, backcross derivatives were obtained with wheat as the recurrent parent.The level of chromosome pairing in A. trachycaulum x wheat, A. yezoense x wheat and wheat x A. junceum hybrids provided no evidence of homologous or homoeologous pairing. Mean pairing frequencies in A. ciliare x wheat, wheat x A. scirpeum and wheat x A. intermedium hybrids indicated homoeologous or autosyndetic pairing. Ph gene was more effective in regulating homoeologous pairing in A. yezoense x wheat hybrids than in A. ciliare x wheat hybrid. Chromosome pairing data of BC1 derivatives indicated that either some of the wheat chromosomes were eliminated or Agropyron chromosomes caused reduced pairing of wheat homologues.

The somatic chromosomes of common wheat, Triticum aestivum L. (2 n = 6x = 42), and those of two of its diploid progenitors and T. speltoides , have been individually identified by a Giemsa staining technique. In wheat, telocentric chromosomes were used to aid the recognition of individual chromosomes, and an ideogram has been constructed depicting the C-band positions. There is no similarity in the C-banding of chromosomes within a homoeologous group, with the possible exception of group 5. Comparisons of the C-banding of the diploid species T. monococcum, T. speltoides , and T. tauschii with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that T. speltoides could not be the donor of the B genome to wheat and that T. monococcum and T. tauschii are the probable donors of the A and D genomes, respectively.

Studies of N-banded mitotic and meiotic karyotypes of Triticum turgidum L. (2 n = 28; AABB) and Triticum timopheevii Zhuk. (2 n = 28; AAGG) and hybrids between them, along with observations of meiotic pairing between telocentrics of the AB-genome chromosomes and their respective homologues and homeologues in T. timopheevii , showed that chromosome 4 (m4) of Triticum monococcum L. is present (as 4A t ) in T. timopheevii but is lacking in T. turgidum . Neither 4A nor 4B pairs with 4A t , but 4A pairs with 4G and, for this reason and because of its banding pattern, must be considered a B-genome chromosome. T. timopheevii chromosomes 4A t and 3A t are involved in a reciprocal translocation, and 2A t , 1G, 2G, and 5G are also involved in translocations. Chromosome arm 4BL occasionally pairs with 7G. The satellites are on the short arms of chromosomes 6A t and 6G of T. timopheevii and 1B and 6B of T. turgidum . It is suggested that ( i ) T. timopheevii orginated as an allotetraploid of Aegilops speltoides Tausch/ T. monococcum and ( ii ) T. turgidum was derived from T. timopheevii by introgressive hybridization with an unknown diploid species, which contributed its distinctive cytoplasm, chromosome 4B or a substantial portion of it, and additional chromosome segments. Rapid fixation of 4B in T. turgidum was ensured by cytoplasm-specific transmission.

Loci detected by Southern blot hybridization of 3,977 expressed sequence tag unigenes were mapped into 159 chromosome bins delineated by breakpoints of a series of overlapping deletions. These data were used to assess synteny levels along homoeologous chromosomes of the wheat A, B, and D genomes, in relation to both bin position on the centromere-telomere axis and the gradient of recombination rates along chromosome arms. Synteny level decreased with the distance of a chromosome region from the centromere. It also decreased with an increase in recombination rates along the average chromosome arm. There were twice as many unique loci in the B genome than in the A and D genomes, and synteny levels between the B genome chromosomes and the A and D genome homoeologues were lower than those between the A and D genome homoeologues. These differences among the wheat genomes were attributed to differences in the mating systems of wheat diploid ancestors. Synteny perturbations were characterized in 31 paralogous sets of loci with perturbed synteny. Both insertions and deletions of loci were detected and both preferentially occurred in high recombination regions of chromosomes.

The use of DNA sequence-based comparative genomics for evolutionary studies and for transferring information from model species to crop species has revolutionized molecular genetics and crop improvement strategies. This study compared 4485 expressed sequence tags (ESTs) that were physically mapped in wheat chromosome bins, to the public rice genome sequence data from 2251 ordered BAC/PAC clones using BLAST. A rice genome view of homologous wheat genome locations based on comparative sequence analysis revealed numerous chromosomal rearrangements that will significantly complicate the use of rice as a model for cross-species transfer of information in nonconserved regions.

Introduction The use of identified monosomic strains in hexaploid wheat inaltes it possible to associate penes for wheat characters with s~ecif ic chromosomes. The U success of this procedure depends on the accuracy bf monosomic identification and on the degree of regularity of chromosome behavior during meiosis in the monosomic plants. Identified monosomic strains were first developed in the hard red spring variety, Chinese Spring, by Sears (1954). These strains were used to differentiate the ltaryotype of Chinese Spring by talting measurements of length and arm ratios of the monosornic chromosomes during meiotic stages (Morrison, 1953; Sears, 1954; Ray and Swaminathan, 1959). As crosses are made between the Chinese Spring monosomic strains and other varieties of common wheat, the ltaryotypes of these varieties can be determined, since the univalent chromosome in the monosomic progeny comes from the variety under study. The effect of the monosoniic condition on the pairing of the other chromosomes can be detected by che frequencies of unpaired chromosomes at metaphase I. i\/lorrison ( 195 3 ) found that hon~ologous chromosomes paired regularly for the most part in eight monosomic strains of Chinese Spring. Person (1956) observed rhe pairing in F, rnonosomic plants from five different crosses, two of which involved Chinese Spring, and in the monosomics from successive bacltcrosses to one of the parental varieties. T h e instability in chromosome pairing was at a peak in the F, monosomics and tended to decrease with each succeed in^ bacltcross to the recurrent parent. b In this investigation F, monosomic plants from crosses between the 2 1 Chinese Spring n~onosomics and the hard red winter variety, Cheyenne, were used to obtain information on the morphology of rhe ~ h e y e n n e chromosome set. The effect of each Cheyenne monosome on pairing of the other chromosomes was determined by recording the frequencies of unpaired chroinosomes at meta~hase I. I The chromosomes are designated by number and genome according to the system suggested by Sears (1958), with additional information from Okamoto (1962). Materials and Methods In 1958 crosses were made in the preenhouse at Lincoln. Nebraslta between U each of the 21 rnonosomic strains of Chinese Spring as female parents and Cheyenne C.I. 8885". The monosomic strains had been obtained from Dr. E. R. Sears, University of i\/lissouri, and the Cheyenne parents came from a source line maintained at the University of Nebraska. The F, generation was planted in the greenhouse in December, 1958.

Feststellung von C-Banden inNigella damascena var. Miss Jekyl mittels eines neuen zytologischen Verfahrens. Es waren 3–5 Chromozentren pro Nukleus zu erkennen.

Gill, B. S., Raupp, W J , Sharma, H. C., Browder, L. E., Hatchett, J. H., Harvey, T. L., Moseman, J. G., and Waines, J G 1986. Resistance in Aegilops squarrosato wheat leafrust, wheat powdery mildew, greenbug, and Hessian fly. Plant Disease 70:553-556. Sixty accessions of Aegilops squarrosa (= Triticum tauschii Schmal) were evaluated for resistance to leaf rust (Paccinia reconditaf. sp. lrirlci) culture PRTUS6; powdery mildew (Erysiphe graminis f. sp. tritici),composite cultures ABK, 127, YUMA CC, and Asosan; greenbug (Schizaphis graminum) biotype E; and Hessian fly (Mayetiola destructor) biotype D. Thirty-two accessrons were resistant to the leaf rust pathogen, 3l to the powdery mildew pathogen, and 34 to the greenbug; 24 were homozygous and I 6 were segregating for resistance to the Hessian fly. Multiple resistance was widespread and six accessions were resistant to both pathogens and both insects Resistance varied from immune to moderate reactions. Because A. squarrosaisthe donor ofthe D genome in common wheat, this species can be readily exploited in breeding wheats for pest resrstance Common or bread wheat (Triticum aestivum L. emend. Thell) is an allohexaploid (AABBDD) of recent origin (about 8,000 yr) between a tetraploid wheat ?i turgidum L. (AABB) and Aegilops squarrosa L. e f. Muschii [DD]) (14). Presumably, initial hybridization was restricted to a narrow range of genotypes of each species, thus the genetic diversity of today's wheats primarily accumulated during the culture and spread of bread wheat into the Mediterranean region, Africa, India, China, and elsewhere. During this expansion. further introgression may have occurred with il, turgidum but not with A. squarrosa because of the latter's strong cross-incompatibility with bread wheat.

Gordon Kimber introduced the workshop topics that were designed to illustrate several facets of genome analysis in higher plants. Kimber's presentation covered genome analysis by chromosome pairing in hybrids. He emphasized that this is the only method in which at least some DNA is sampled along the entire length of the chromosomes. Moreover, originally based on total pairing, genome analysis has now been extended to include numerical assessments of the patterns of pairing. Genome analysis is most accurate in those hybrids where there is pairing competition; for example in diploid x allopolyploid hybrids. There are various models of pairing at increasing levels of ploidy that can be used to calculate relative measures of affinity among the genomes. In the ensuing discussion,, Kimber pointed out that genes affecting chromosome pairing do not alter the results of genome analysis as they influence overall pairing, but not the pattern of pairing. Limitations to genome analysis were also discussed. For example, chromosome pairing in diploid hybrids cannot be considered a reliable indication of relationship because of lack of competition for synaptic partners. Similarly, plants with small chromosomes are also unsuitable for genome analysis as differences between rod and ring bivalents cannot be distinguished. Second speaker, B. S. Gill, spoke on the use of heterochromatin banding and in situ hybridization in assaying subgenomic affinities. These techniques provide additional and complementary information to genome analysis by chromosome pairing. The subgenomic affinities that can be assayed include individual chromosome and chromosome arm homologies and specific DNA sequence homologies. Individual chromosome homologies have been assessed by banding analysis of metaphase I configurations in meiocytes. Somatic chromosome banding analysis provides additional information on the amount, location, and structure of heterochromatin. In situ hybridization has been used to study the amount and location of specific DNA sequences in different genomes. Such marked chromosomes can be traced in natural and experimental introgressive hybridization studies. Southern blotting analysis with defined DNA sequences (rDNA, as an example) at different 'stringencies of hybridization can be used to discern evolutionary relationship among taxa. The questions involved strategies for cloning of DNA sequences for molecular cytogenetics analysis. The third speaker, K. Tsunewaki described the role of plasmon analysis as a means of identifying cytoplasm donor to polyploid species. Cytoplasm of various Aegilops species have been substituted with the nucleus of Triticum aestivum. From the phenotypes of such alloplasmic lines, it has been possible to trace diploid donor of cytoplasm of polyploid Triticum and Aegilops species. More recently, restriction digestion analysis of chloroplast and mitochondrial DNA has been used for assaying cytoplasmic affinities. Some of the problems with the use of plasmon analysis in phylogenetic affinities were discussed. First of all, there is intraspecific variation in both mitochondrial and chloroplast DNAs. Another potential problem is the male transmission of cytoplasmic organelles, although in wheat no such male transmission has been documented. The final speaker, D. F. Weber, discussed the use of restriction fragment length polymorphisms (RFLPs) in corn improvement. He elaborated on the methodology and applications of RFLP analysis. In addition to their use as molecular markers, RFLPs are also useful in uncovering single gene or small chromosomal duplications or other aberrations that cannot be detected by pairing analysis. About 400 RFLP loci have been mapped in corn. About 20 % of the loci were found to be duplicated either on the same chromosome or were dispersed on many chromosomes. The A-B translocations were useful in chromosome arm assignment of RFLP loci, in mapping of centromeres, and in aligning RFLP linkage maps with chromosome maps and conventional linkage maps. There was considerable discussion on the advancement of RFLP maps in different taxa. It was suggested that there should be a coordination of the work on RFLP maps and on comparative gene mapping. Annual meetings of the Genetics Society of Canada or America could provide forums for joint meetings of RFLP workers in plants. The workshop ended on a note of thanks by Kimber to participating speakers and the audience. About 60 people participated and the workshop was considered a success.