Study of a translocation in diploid rye

A cytological study of a large reciprocal translocation between chromosome V and VI inSecale cereale is reported. The translocation is identifiable both in root-tip squashes and at various stages of meiosis in pollen mother cells. The ease in identification, high fertility, and uniform behaviour irrespective of summer or winter background in diploid rye, makes this interchange a favourable standard stock for identification of other translocations and their use in a program of gene-location.     

Chiasma distribution in rye chromosomes of diploid rye and in wheat/rye addition lines in relation to C-heterochromatin

Summary In five genetically different inbred lines of rye and in the seven Chinese Spring/Imperial wheatrye addition lines, chiasma distribution in rye chromosomes was studied with respect to the amount and position of constitutive heterochromatin (Giemsa C-bands). In all inbred lines, rye chromosomes with one primary terminal band were more frequently found as univalents than those with primary bands on both telomeres. These chromosomes were most probably 5R and/or 6R. In the addition lines a highly significant reduction in the number of arms bound by chiasmata was found for rye chromosomes 5R and 6R. Because of the similar chiasma distribution in the inbred lines and in the rye chromosomes of the addition lines, no effect of the wheat genome on the number of chiasmata in the rye chromosomes can be ascertained. However, a relationship between chiasma frequency and chromosome arm length seems to exist, since under reduced chiasma conditions the two shortest arms of the rye complement, those of chromosomes 5R and 6R, frequently fail to form a chiasma. No effect of the large blocks of constitutive heterochromatin in the telomeres of the rye chromosomes on the position of chiasmata within a bivalent could be established.This study was financially supported by the Deutsche Forschungsgemeinschaft     

Chiasma formation in duplicated segments of the haploid rye genome

In meiosis of haploid rye associations of two or more chromosomes are observed. In order to investigate whether these associations are chiasmate, metaphase I and anaphase I associations were analysed after Giemsa banding. — At anaphase I chromatid exchanges between differently marked chromosome arms were observed, which proved the presence of real chiasmata. The association between banded and unbanded arms shows that the heterochromatic telomeres do not act as secondary pairing sources. Different statistical approaches were used to test randomness of chiasma formation. It appeared to be non-random, which showed that the segments involved were non-randomly located and probably limited in number. The nature of these segments is discussed.     

A translocation heterozygote in garden Canna

A case of translocation heterozygosity has been discovered in gardenCanna. Morphologically the heterozygote is distinctive, being a pygmy type with small flowers which do not open. Cytologically it shows a ring or a chain of 4 plus 7 bivalents. The present observations reveal that rings disjunct usually in adjacent, and chains in an alternate manner. The subsequent course of meiosis is normal. The variety is totally sterile both after self and cross pollination. It has very likely arisen as a hybrid between two parents differing in one interchange.     

Genetics of rye phosphatases: evidence of a duplication

Summary Genetic analyses were conducted on alkaline phosphatases of the endosperm of dry kernels and leaf acid phosphatases in four open pollinated and one inbred line of cultivated rye (Secale cereale L.). A total of seven alkaline phosphatase isozymes were observed occurring at variable frequencies in the different cultivars analyzed. We propose that at least five loci control the alkaline phosphatases of rye endosperm — Alph-1, Alph-2, Alph-3, Alph-4 and Alph-5 — all of which have monomeric behaviour. The leaf acid phosphatases are controlled by one locus and have a dimeric quaternary structure. All loci coding for alkaline phosphatase isozymes showed one active, dominant allele and one null, recessive allele, except for the locus Alph-3 which showed two active, dominant alleles and one null, recessive one. The linkage analyses suggest the existence of two linkage groups for alkaline phosphatases: one of them would contain Alph-2, Alph-4, Alph-5 and the locus/loci coding isozymes 6 and 7. This linkage group is located in the 7RS chromosome arm. The other group would include Alph-1 and Alph-3 loci, being located in the 1RL chromosome arm. Leaf acid phosphatases have been previously located in the 7RL chromosome arm. Our data also support an independent relationship between loci controlling the endosperm alkaline phosphatases and leaf acid phosphatases.     

Trisomy greatly enhances interstitial crossing over in a translocation heterozygote of Secale

Chromosomal rearrangements, including reciprocal translocations, may prevent recombinational transfer of genes from a donor genotype to a recipient, especially when the gene is located in an interstitial segment. The effect of trisomy of chromosome arm 1RS on recombination was studied in translocation heterozygote T248W of rye ( Secale cereale ), involving chromosome arms 1RS and 6RS. (Pro)metaphase I configuration frequencies were analyzed. Crossing over, estimated as chiasma parameters, in five genetically different euploid heterozygotes was compared with those of 10 different single arm trisomics. The addition of 1RS greatly altered the crossing over pattern around the translocation break point, with a special increase in the interstitial segment of 6RS and adjoining regions, normally hardly accessible to recombination. Furthermore, there was considerable variation between plants of closely related genotypes. Heterogeneity widens the distribution of crossing overs, including segments normally not accessible to recombination, but decreases average recombination in other segments. The extra chromosome and abnormal segregants are eliminated by using the trisomic as the pollen parent.     

Laboratory evalution of a translocation double heterozygote for genetic control of Aedes aegypti

Summary Two pure translocation homozygote stocks, T₁/T₁ and T₃/T₃, were used to produce a double translocation heterozygote system designated T₁/T₃, employing T₁/T₁ as the male and T₃/T₃ as the female parent. The double heterozygote showed 73 % sterility when mated to wild females. Tests on mating competitiveness, recombination frequency in the differential segment, insemination rate and inheritance of sterility after release, for four generations in laboratory cages, have been carried out to evaluate the efficiency of this strain as an agent for a population control programme.     

Production of a new wheat line possessing the 1BL.1RS wheat-rye translocation derived from Korean rye cultivar Paldanghomil

The 1BL.1RS translocations between wheat (Triticum aestivum L.) and rye (Secale cereale L.) are widely used in bread wheat breeding programs, but all modern wheat cultivars with the 1BL.1RS have shown genetic vulnerability due to one rye source – a German cultivar, Petkus. We have developed, a new 1BL.1RS wheat-rye translocation line from the backcross of the F₁ hybrid of wheat cv. Olmil and rye cv. Paldanghomil, both cultivars from Korea. The GISH technique was applied to identify the presence of rye chromatin in 467 BC₁F₆ lines selected from 77 BC₁F₅ lines. Only one line, Yw62–11, showed wheat-rye translocated chromosomes, with a somatic chromosome number of 2n=42. C-banding patterns revealed that the translocated chromosome was 1BL.1RS, showing prominent bands in the terminal and sub-terminal regions of the short arm as well as in the centromeric region and terminal region of the long arm. This new 1BL.1RS translocation line formed 21 bivalents like common wheat at meiotic metaphase I, thereby showing complete homology. Received: 28 February 2001 / Accepted: 17 April 2001     

Chromosomal translocation and segmental duplication in Cryptococcus neoformans

Large chromosomal events such as translocations and segmental duplications enable rapid adaptation to new environments. Here we marshal genomic, genetic, meiotic mapping, and physical evidence to demonstrate that a chromosomal translocation and segmental duplication occurred during construction of a congenic strain pair in the fungal human pathogen Cryptococcus neoformans. Two chromosomes underwent telomere-telomere fusion, generating a dicentric chromosome that broke to produce a chromosomal translocation, forming two novel chromosomes sharing a large segmental duplication. The duplication spans 62,872 identical nucleotides and generated a second copy of 22 predicted genes, and we hypothesize that this event may have occurred during meiosis. Gene disruption studies of one embedded gene (SMG1) corroborate that this region is duplicated in an otherwise haploid genome. These findings resolve a genome project assembly anomaly and illustrate an example of rapid genome evolution in a fungal genome rich in repetitive elements.     

Centromere co-orientation in a spontaneous translocation heterozygote of Euchorthippus pulvinatus gallicus (Acrididae,Orthoptera)

The co-orientation of a quadrivalent in an individual of E. pulvinatus gallicus heterozygous for a reciprocal translocation is studied. The data agree with the hypothesis that the co-orientation behaviour of two adjacent centromeres in a quadrivalent depends on the relative distance between them at metaphase I, this distance being determined by chiasmata.     

Successive spontaneous abortions with diverse chromosomal aberrations in human translocation heterozygote.

A patient who had 3 first-trimester spontaneous abortions (blighted ova) was found to be carrying a balanced 13/14 Robertsonian translocation. In the 2 cases cytogenetically analyzed, different chromosomal aberration were found (trisomy 16 and supernumerary D elements). Histologic examination of the placentas of all 3 abortions revealed hypovascular or avascular villi, hydropic degeneration, and occasional atypical stromal (Hofbauer-like) cells. In 2 cases the decidua was examined by light microscopy and was diffusely inflamed with a plasmolymphocytic infiltrate. The relation of the maternal translocation to the repeated abortions with chromosome anomalies is discussed.     

Identification of the chromosomes of the rye translocation tester set

Summary Intercrossing the Wageningen translocation tester set of rye and the series of Imperial rye additions to Chinese Spring wheat of Sears yielded 29 chromosome disomic translocation hybrids. Observation of trivalents led to the identification of the chromosomes of the tester set in terms of the terminology system used in the Triticinae. The analysis was complicated by very low chiasma frequencies in some short chromosome segments in the hybrids. Nevertheless, it could be safely concluded that 1R=VII; 2R=III; 3R=II; 4R=IV; 5R=VI; 6R=V; 7R=I, which deviates slightly from previous classifications based on other methods.     

Chiasma distributions and chromosome segregation in male and female translocation heterozygous mice analysed using FISH

Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a translocation [T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations. However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata, also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice. The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was not the case for T(7;16)67H. Received: 6 June 1998 / Accepted: 9 October 1998