Chromosome morphology and cytomolecular characteristics of the perennial rye cultivar ‘Kriszta’

The perennial Secale cereanum cultivar ‘Kriszta’ is an artificial hybrid of S. cereale and S. strictum ssp. anatolicum. From the cross between the wheat line Mv9kr1 and ‘Kriszta’, which aimed the transfer of beneficial traits from rye to wheat, numerous translocation lines have been produced. For the identification of the translocated chromosomes, the unambiguous differentiation between chromosome arms of ‘Kriszta’ is essential. The identification of its short chromosome arms using conventional FISH probes is easy, but because of their similar hybridization patterns, its long arms cannot be distinguished. The present study aimed to create the detailed karyotype of ‘Kriszta’, especially that of long arms, by both chromosome measurements and FISH using highly repetitive, as well as subtelomeric tandem repeat, and synthetic microsatellite DNA sequences. Our results indicate that the chromosome complement of ‘Kriszta’ is not a simple combination of the chromosomes of the parental rye species but is composed of rearranged chromosomes. It is also showed that an adequate pair-wise combination of the DNA sequences pSc119.2, pSc200, pSc250, and (AAC)5 makes it possible to identify any of the long arms of S. cereanum cv. Kriszta chromosomes. The future usability of the identified wheat- ‘Kriszta’ translocated chromosomes is also discussed.

Double Helix Structure and Finite Persisting Sphere Genetic Algorithm in Designing Digital Circuit Structure

This paper proposes a new approach of chromosome representation in digital circuit design which is Double Helix Structure (DHS). The idea of DHS in chromosome representation is inspired from the nature of the DNA's structure that built up the formation of the chromosomes. DHS is an uncomplicated design method. It uses short chromosome string to represent the circuit structure. This new structure representation is flexible in size where it is not restricted by the conventional matrix structure representation. There are some advantages of the proposed method such as convenience to apply due to the simple formation and flexible structure, less requirement of memory allocation and faster processing time due to the short chromosomes representation. In this paper, DHS is combined with Finite Persisting Sphere Genetic Algorithm (FPSGA) to optimal the digital circuit structure design. The experimental results prove that DHS uses short chromosome string to produce the flexible digital circuit structure and FPSGA further optimal the number of gates used in the structure. The proposed method has better performance compared to other methods.

Chromosomal fragment responsible for genetic mosaicism in larval body marking of the silkworm, Bombyx mori

SummarySeveral genetic mosaics for larval body marking of the silkworm, Bombyx mori, have been induced by X-ray irradiation. It is hypothesized that the occasional loss of chromosomal fragments carrying the genes for body marking during development may give rise to this type of mosaicism. Using pulsed field gel electrophoresis (PFGE), we find that a DNA molecule of about 2·5 megabases (Mb) is present in one type of mosaic (mottled striped strains pSm788 and pSm872), and not in any other strain. This DNA fragment hybridizes strongly with some chorion genes which are less than 6·9 cM away from the ps locus, and hence it corresponds to a chromosomal fragment containing genes for both striped marking (ps) and the chorion. In the non-mottled ps strain, the phenotype before X-ray irradiation, no band was detected either on a PFGE gel or after hybridization with the chorion probe. These results suggest that the mottled ps strains carry short chromosome fragments which are lost differentially during cell divisions.

Meiotic crossing-over between sites on opposite sides of the centromeres of homoeologues is frequent in hybrid Aloeaceae

During meiosis, long and short arms of acrocentric homoeologues pair and cross over in the centromere region in 95 (66.9%) of 142 hybrids of differing parentage in the monocotyledon family Aloeaceae. A characteristic configuration, the L–S bridge, is produced at anaphase I with frequencies ranging from <1 to 48% of pollen mother cells and in up to three bivalents per pollen mother cell. Too frequent to be due to inversion hybridity, L–S crossing-over most probably results from straight, noninverted pairing between nonhomologous proximal segments of the long and short chromosome arms following centromere mismatching in the heteromorphic bivalents. It is suggested that there are several lengths of DNA in different regions of homoeologous chromosomes, but perhaps concentrated around the centromere, that are sufficiently similar to recognize each other, pair, and cross over when brought together in a heteromorphic bivalent with mismatching of centromeres.Key words: Aloeaceae, hybrid, meiosis, nonhomologous pairing, crossing-over.

Cytogenetic analysis of interspecific hybrids and amphiploids between two diploid crested wheatgrasses, Agropyron mongolicum and A. cristatum

Agropyron mongolicum Keng, the narrow linear-spiked diploid species (2n = 14), was hybridized with the broad pectinate-spiked diploid (2n = 14), A. cristatum (L.) Gaertner. The F1 hybrids were all diploids and morphologically intermediate to their parents. Chromosome pairing at metaphase I in the hybrids averaged 1.40 I, 5.59 II, 0.35 III, and 0.09 IV per cell, demonstrating that the two parental genomes are very similar. The F1 hybrids were partially fertile. The F2 progeny showed a broad array of variations in spike morphology and chromosome pairing behavior. Cytological data of the F1 hybrids and the F2 progeny revealed that these two diploid species contain the same basic P genome but differ by structural rearrangements of some chromosomes. The patterns of multivalent associations were the result of a heterozygous reciprocal translocation between a long and a very short chromosome segment. The colchicine-induced C0 amphiploids were fully fertile with regular chromosome pairing behavior. These two diploid species are the likely source of morphological variation in the tetraploid crested wheatgrasses.Key words: Agropyron, cytogenetics, chromosome pairing, interspecific hybrids.

An assessment of preferential chromosome pairing at meiosis in Dactylis glomerata

Meiosis was analyzed in 26 full-sib genotypes of tetraploid orchard grass (Dactylis glomerata L., 2n = 4x = 28) that had given apparently nontetrasomic segregation for reaction to the stem rust fungus, Puccinia graminis Pers. f. sp. dactylidis Guyot et Massenot. The mean chromosome associations were 0.24 I, 1.64 rod II, 6.47 ring II, 0.05 III, 0.85 chain IV, and 1.99 ring IV. Optimizations for two classes of mathematical models showed an appreciable excess of bivalents over the number expected upon independent association of long and short chromosome arms. The most probable cause of this bivalent excess was preferential pairing due to slight genomic differentiation in an autotetraploid background. Excess bivalents may have also arisen from close proximity of the two ends of each chromosome upon initiation of pairing. Inequality of chiasma formation between long and short chromosome arms was a minor contributor of excess bivalents. Because of independent segregation of homologous groups, some sibs fit the Kimber–Alonso 2:2 model best, others the 2:1:1.

Prediction and analysis of spatial order in haploid chromosome complements

Bennett has proposed a model that predicts a mean ordered arrangement of all the chromosomes in a simple haploid genome, based on associations of pairs of most similar long, and pairs of most similar short, chromosome arms. The model orders a complete simple haploid genome so that each chromosome is associated with two constant neighbours. This paper describes a test of the model with two types of data obtained from the same reconstructed serially sectioned somatic metaphases examined in the electron microscope. First, chromosome arm volumes were estimated and used to identify the chromosomes and to predict their mean spatial order. Secondly, centromere positions in three dimensions were established. In the species and hybrids used, all with 14 chromosomes, there are so many ways of positioning the chromosomes within haploid sets that a computer-aided analysis was developed. With use of only centromere identities and positions, the programs generated all possible orders of centromeres in haploid sets (where each centromere has two neighbours) and computed the sum of distances between centromeres for each order within a cell. Orders were ranked in ascending sequence of sums of distances. Orders that ranked highest were taken as ‘best’. After results for replicate cells had been pooled, orders were ranked from best to worst. A test of the predicted order was then made by finding its position on this summary. In all the four grasses examined, the predicted order was among the 5% of orders judged best by the analysis. To demonstrate and confirm the predicted order in these grasses, only seven to ten reconstructed nuclei were required. Presumably this test is suitable for general application to other materials whose simple haploid genomes contain between six and about ten biarmed chromosomes.