Dosage effect of a gene with a regulating effect on anthocyanin synthesis in a trisomic Petunia hybrida

A Petunia hybrida inbred line (W 28) has white flowers with red spots on the corolla. These spots are the result of back mutations of an unstable allele of the gene Anl for anthocyanin synthesis. Among the progeny of a population of selfed plants a primary trisomic with red-spotted white flowers was found. The reversion frequency was more than twice as high as compared with disomic plants of the same family.It was found that the chromosome in triplicate was not the chromosome on which the gene Anl is localized. It can be concluded that there is an independently segregating factor which influences the frequency of back mutations of the Anl locus. Twin spots were found among the flowers of the trisomic. They consisted of two adjacent sectors, one with a spot frequency equal to that of the flowers of disomic plants, and the other with a spot frequency more than twice as high as that of the trisomic. Probably an irregular distribution of the extra chromosome resulted in one sector with the normal diploid number of chromosomes, and an adjacent sector with two extra chromosomes. The reversion frequencies in the sector suggest that the factor which affects the reversion frequency of the unstable alleles of Anl exhibits a dosage effect.     

Cytogenetics of an unstable trisomie in barley (Hordeum vulgare).

The origin, identification, meiotic chromosome behavior, and breeding behavior of an unstable trisomic barley were studied. The extra chromosome originated by breakage and fusion of an acrocentric chromosome 3 in a plant from an F2 population of a cross between acrotrisomic 3L3S (2n = 14 + 1 acro3L3S) and a balanced lethal stock, xc. (xantha) ac (albino). The F2 population segregated only for the albino trait. The genotypic constitution of the trisomic plant was ac ac (for both normal chromosome 3) and Ac (for the unstable metacentric chromosome). The unstable extra metacentric chromosome was designated as metacentric 3B (abbreviated as meta3B). Meiotic chromosome behavior in plants with 2n = 14 + 1 meta3B differed from plant to plant and within spikes. Some plants showed only trisomic cells with a chromosome configuration of 1 III + 6 II and 7 II + 1 I at metaphase I, whereas other plants showed both trisomie and disomic cells (7 II) that resulted from the elimination of the extra meta3B. The frequency of ring trivalents was low (6.8%). An average transmission rate of unstable meta3B ranged from 4.3 to 12.9%. The elimination of meta3B, and hence loss of the dominant Ac allele, resulted in albino seedlings as well as white stripes on plants, leaves, and spikes. Chromosome numbers of albino seedlings in the progeny of 2n = 14 + 1 meta3B were all diploid (2n = 14), while green seedlings contained 2n = 14 + 1 meta3B. However, progenies of some spikes of one trisomic plant showed a low frequency of green diploids and metatrisomics (2n = 14 + 1 meta3B), which was attributed to crossing-over.     

Primary trisomics of rice: origin, morphology, cytology and use in linkage mapping

Twelve primary trisomics of Oryza sativa L. were isolated from the progenies of spontaneous triploids and were transferred by backcrossing to the genetic background of IR36, a widely grown high yielding rice variety. Eleven trisomics can be identified morphologically from one another and from diploids. However, triplo 11 is difficult to distinguish from diploid sibs.—The extra chromosome of each trisomic was identified cytologically at pachytene stage of meiosis, and the chromosomes were numbered according to their length at this stage. The major distinguishing features of each pachytene chromosome were redescribed.—The female transmission rates varied from 15.5% for triplo 1, the longest chromosome, to 43.9% for triplo 12, the shortest chromosome. Seven of the 12 primary trisomics transmitted the extra chromosome through the male. The low level of chromosomal imbalance tolerated by rice and other evidence are interpreted to indicate that this species is a basic diploid.—Genetic segregation for 22 marker genes in the trisomic progenies was studied. Of a possible 264 combinations, involving 22 genes and 12 trisomics, 120 were examined. Marker genes for each of the 12 chromosomes were identified. The results helped establish associations between linkage groups and cytologically identifiable chromosomes of rice for the first time. Relationships between various systems of numbering chromosomes, trisomics, linkage groups and marker genes are described, and a revised linkage map of rice is presented.     

Meiosis in four trisomic and one double trisomic males of the newt Pleurodeles waltlii

In the newt Pleurodeles waltlii, meiosis was studied in four trisomic and one double trisomic males. Study of first prophase shows that trivalent frequencies and trivalent configurations are correlated with chromosome length; moreover, trivalent configurations indicate that long chromosomes have multiple points of initiation of synapsis whereas two points might be adequate to secure synapsis of short chromosomes. From the study of metaphase II it appears that the extra chromosomes segregate in half of the spermatocytes II. Some abnormal spermatocytes, resulting from nondisjunction of chromosomes at mitosis or at first division of meiosis, or from precocious division of chromosomes at first division of meiosis were observed. In the male double trisomic meiosis fails at anaphase of second division; this accounts for the sterility of the individual.     

Aneuhaploids and tetrasomics in rice (Oryza sativa L.) derived from anther culture of trisomics.

Eight types of aneuhaploids (Aneuhaplo 4, 5, 6, 8, 9, 10, 11, and 12) and eight types of tetrasomics (Tetraplo 4, 5, 6, 7, 8, 9, 10, and 12) of rice have been obtained from anther culture of trisomics. This paper reports the plant morphology of these aneuploids and their chromosome behavior at metaphase I. Aneuhaploids for different chromosomes are distinguishable from each other and are morphologically similar to the parental trisomics, suggesting that the extra chromosome has similar genetic effects on plant morphology at the haploid level as at the diploid level. Similarly, tetrasomics with different extra chromosomes are distinguishable from each other and are similar morphologically to the parental trisomic. However, stronger changes in morphological characters were observed in tetrasomics compared with trisomics having the same extra chromosome, as a result of a dosage effect of the extra chromosomes. Comparing plant size between aneuhaploid, tetrasomic, and trisomic with the same extra chromosome, it was shown that the trisomic was the largest, the tetrasomic was of medium size, and the aneuhaploid was the smallest, except for those plants with an extra chromosome 8 in which plant size is dramatically decreased in both the aneuhaploid and the tetrasomic. At metaphase I, aneuhaploids showed chromosome configurations of 1 II + 11 I and 13 I. The frequency of the 1 II + 11 I configuration is higher than 70%, indicating that homologous chromosomes in aneuhaploids tend to stay associated in meiosis. Intragenome chromosome pairing (2 II + 9 I), so called secondary association, was observed in the aneuhaploid for chromosome 5. Tetrasomic plants showed 5 kinds of chromosome configurations: 1 IV + 11 II, 1 III + 11 II + 1 I, 13 II, 12 II + 2 I, and 11 II + 4 I. A chromosome configuration of 13 II was often observed in tetrasomics with shorter extra chromosomes and a chromosome configuration of 1 IV + 11 II was often observed in tetrasomics with longer extra chromosomes. Aneuhaploids had complete seed sterility. Tetrasomics showed very poor pollen fertility and complete seed sterility, except for a few shriveled seeds that were observed in Tetraplo 6 and 9. This is the first report in rice where many aneuhaploids and tetrasomics have been characterized. This information will help to further unravel rice aneuploidy and cytogenetics. The aneuploids obtained here will be very useful tools for the study of genetics and breeding in rice.     

Trisomics from triploid-diploid crosses in self-incompatible Lycopersicum peruvianum

Summary An attempt was carried out to produce trisomics of the wild tomato L. peruvianum, to define their essential features, and to detect relationships between trisomy and the expression of self-compatibility.Triploid-diploid crosses in L. peruvianum yielded nearly 40% aneuploids. Of these, 18% were single trisomics, and the rest had 2, 3 and 4 extra chromosomes. Almost all the trisomics occurred in crosses where the triploid was used as female parent. Vigour and fertility of trisomics were not much different from those of disomics, and morphologically they were very similar.The extra chromosome was identified in three self-compatible trisomic plants through somatic and pachytene chromosome morphology. One of these plants was trisomic for chromosome 1, while the other two were trisomic for chromosome 3. In these trisomics a positive correlation was found between chromosome length and trivalent formation, but no relationship between chromosome length and frequency of laggards was observed.A series of test-crosses revealed that the capacity of the trisomics to produce seed upon selfing always resulted from alterations of the incompatibility phenotype of the style and not from competitive interaction in the pollen. Progeny analyses showed that the self-compatibility features of the trisomics were not transmitted from one generation to the next. The implications of these findings are discussed.This work has been supported by a contract between the European Communities and the CNEN. This publication is contribution no. 1458 from the Biology Division of the European Communities and contribution no. 472 from the Divisione Applicazioni delle Radiazioni del CNEN.     

Tertiary trisomics in pearl millet (Pennisetum typhoides Stapf & Hubb)

Four tertiary trisomic plants are reported here, two of them (Nos. Tr11 and Tr13) from selfed progeny of a triploid Pearl millet and the other two (Nos. 3/12 and 16/7) from the progenies of radiation induced interchange heterozygotes. The extra chromosome in Tr13 and 3/12 was the nucleolus organizing chromosome. In No. 16/7 an extra chromosome enters into an association chromosomes were also involved. Meiotic behaviour in these four trisomics indicates that Tr11 and 3/12 are tertiary trisomics. It is suggested that two reciprocal translocations have occurred between two sets of chromosomes in the triploid parent and that syngamy has taken place in such a way that four interchange chromosomes and one non-interchange nucleolus organizing chromosome have come together in the offspring. The extra chromosome in No. 16/7 is an interchange chromosome which is homologous to one of the chromosomes of an interchange complex of six chromosomes.     

Tertiary trisomics in the garden pea as a model of B chromosome evolution in plants

It is hypothesized that, in plants, genetically empty B chromosomes may originate from the extra chromosome (E) of tertiary trisomics if (i) the region of basic chromosomes homologous to the E (H-region) harbors a sporophytic lethal covered by the wild-type allele in E, and (ii) crossing-over between E and the H-region is suppressed. Under these conditions, most loss-of-function mutations occurring in the H-region are deleterious for haploid gametophytes, whereas those occurring in E are neutral or advantageous for hyperploid (n+1) gametophytes. As a result, natural selection at the gametophyte level can lead to the degeneration of E, leaving the H-region intact. Using Hammarlund translocation T(3-6)a, we synthesized two trisomic lines of the garden pea (Pisum sativum L.), where E was composed of the short arms of chromosomes 3 and 6 and the H-region carried recessive markers. In the trisomic line TRIS, we found few crossovers between E and the H-region. In the trisomic line TRUST, obtained after a change of basic chromosome constitution, recombination in this region was completely suppressed. After induction in the H-region of TRUST of a recessive sporophytic mutation rmv, two 15-chromosome lines of stable trisomics were established. One of them passed 11 generations, having produced more than 6000 individuals, all of them trisomic, and E remained present as a single element with no pairing partners. No tetrasomics were detected in these lines. If such trisomics occurred in nature, their extra chromosomes are likely to become a B chromosome.     

Translocation t(11;14) and trisomy 11q13----qter in multiple myeloma

A 14q+ marker with extra material derived from chromosome 11 long arm, i.e. segment q13----qter, has been found in cells from a pleural effusion in a patient with highly malignant multiple myeloma. The segment 11q13----qter was trisomic because of the presence of both apparently normal homologous chromosomes 11.     

Development and applications of a complete set of rice telotrisomics

We previously isolated a complete set of primary trisomics along with many other aneuploids from triploid plants derived from an indica rice variety "Zhongxian 3037." About 30,000 progeny from these trisomic and aneuploid plants were grown each year from 1994 to 1999. The variants that differed morphologically from both the diploids and the original primary trisomics were collected for cytological identification. From these variants, a complete set of telotrisomics covering all 24 rice chromosome arms was obtained. The identities of the extra chromosomes were further confirmed by dosage analysis of the RFLP markers on extra chromosome arms. The telocentric nature of the extra chromosomes in these stocks was verified by fluorescence in situ hybridization (FISH) using a rice centromeric BAC clone as a marker probe. In general, the shorter the extra chromosome arm of a telotrisomic, the stronger the resemblance it bears to the diploid; the longer the extra chromosome arm, the stronger the resemblance to the corresponding primary trisomic. We demonstrated that DNA clones can be rapidly assigned to specific chromosome arms by dosage analysis with the telotrisomics. We also showed that telotrisomics are valuable tools for chromosome microdissection and for developing chromosome-specific DNA markers.     

Genetic Control of Chromosome Elimination during Haploid Formation in Barley

Genetic control over chromosome stability in the interspecific hybrid embryos of Hordeum vulgare and H. bulbosum has been hypothesized to reside on specific chromosomes. In this study, crosses between the primary trisomic lines for the seven different H. vulgare chromosomes and tetraploid H. bulbosum revealed that both chromosomes 2 and 3 of H. vulgare were involved in the control of chromosome elimination. Subsequent crosses using the available monotelotrisomics for chromosomes 2 and 3 led to the conclusion that both arms of chromosome 2 and the short arm of chromosome 3 most likely contain major genetic factors.—From the results of this study and the genome balance observed in the interspecific crosses between H. vulgare and H. bulbosum at the diploid and tetraploid cytotypes, it appears that the factors causing the elimination of the bulbosum chromosomes are located on the H. vulgare chromosome. These factors are offset or balanced by factors on the H. bulbosum chromosomes which, when present in sufficient dosage, either neutralize the effects of the vulgare factors or are able to "protect" the bulbosum chromosomes.     

TRISOMIC TRANSMISSION IN CLARKIA UNGUICULATA

Vasek , F. C. (U. California, Riverside.) Trisomic transmission in Clarkia unguiculata. Amer. Jour. Bot. 48(9): 829–833. 1961.—Seven primary trisomic plants derived from a triploid-diploid cross were self-pollinated. The 7 progenies included diploids and trisomics, the latter varying in frequency from 16 to 30%. In addition, 2 of the progenies included tetrasomic plants. Crosses were made between diploids and either trisomics or tetrasomics. The extra chromosome of 1 progeny was readily transmitted through the pollen of trisomic and tetrasomic plants. When a trisomic of the same progeny was used as a seed parent, only diploids and tetrasomics were found among the offspring, indicating a duplication of the extra chromosome. The extra chromosomes of other progenies were not transmitted through either pollen or eggs in controlled diploid-trisomic crosses but trisomics of these progenies were recovered after self-pollination. It is suggested that differential pollen-tube growth precluded transmission to diploid-trisomic hybrids and that under conditions of reduced pollen competition the extra chromosome normally would be transmitted through pollen. The extra chromosomes generally occur as univalents at metaphase and are ordinarily included in telophase nuclei.     

Association of the extra chromosome of tertiary trisomic male mice with the sex chromosomes during first meiotic prophase,and its significance for impairment of spermatogenesis

Pachytene nuclei were studied in five tertiary trisomic male mice of Ts(1¹³)70H and two of Ts(5¹²)31H, with special attention given to the sex vesicles. Silver stained air dried cells analysed by light microscopy were used mainly, but in addition one sample of surface spread, ethanolic phosphotungstic acid stained nuclei was analysed by electron microscopy. With both techniques and both karyotypes, the extra chromosome (or the greater part of it) almost consistently aggregated with the sex chromosomes. Thereby, the chromatin structure of the extra chromosome as judged by a fine granular appearance resembled that of the sex chromosomes. The animals used ranged from almost azospermic to fertile oligospermic. This variation was not reflected in the position and morphology of the chromosomes 1¹³ and 5¹². — Using the whole mount spreading EM technique within a Ts(1¹³)70H tertiary trisomic, both 13;13;1¹³ trivalents and 1¹³ univalents were observed. The 13;13;1¹³ trivalents showed a variety of morphologies, ranging from a situation showing classical partner exchange to complete synapsis between the two 13 homologues with the 1¹³ telomeric region adhering. The latter configuration is thought not to lead to chiasma formation.     

Maize tertiary trisomic stocks derived from B-A translocations

Reciprocal translocations between supernumerary B chromosomes and the basic complement of A chromosomes in maize have resulted in a powerful set of tools to manipulate the dosage of chromosomal segments. From 15 B-A reciprocal translocation stocks that have the B-A chromosome genetically marked we have developed tertiary trisomic stocks. Tertiary trisomics are 2n + 1 aneuploids where the extra chromosome is a translocation element, in this case a B-A chromosome. Whereas B-A translocations produce aneuploidy in the sperm, the tertiary trisomic plant efficiently transmits hyperploid gametes maternally. Because the B-A tertiary trisomic stocks and the B-A translocation stocks from which they were derived are introgressed into the W22 inbred line, the effects of maternally and paternally transmitted trisomic B-A chromosomes can be compared. Data are presented on both the male and female transmission rates of the B-A chromosomes in the tertiary trisomic stocks.     

Cytological identification of the chromosomes involved in Nishimura's rice translocation lines

During the past three decades, Nishimura's reciprocal translocation lines of rice have been used in rice cytogenetics to locate genes on chromosomes, to number extra chromosomes of trisomic series and to associate individual linkage groups with specific chromosomes. In this report, we present our identification of the chromosomes involved in 11 of Nishimura's translocation lines using both meiotic pachytene and mitotic prometaphase chromosome analysis. In addition, the numbering of the 12 linkage groups suggested by Nagao and Takahashi, and modified later by many workers, has been revised to agree with the numbering of the identified chromosomes.     

Comparison of the transmission of three trisomies by males and females in the newt Pleurodeles waltlii (author's transl)]

In the newt Pleurodelles waltlii, males and females trisomic for chromosomes 8, 10 and 11 are fertile. Crosses between such trisomics and diploids were carried out. Progeny analysis showed that an extra chromosome is transmitted to half of the gametes of both males and females trisomics. The extra chromosome apparently causes interference in the regular mechanics of meiotic division, so that trisomics throw nonparental aneuploids and polyploids in their progenies. Moreover, some descendants develop chromosome anomalies during embryonic life ; thus, the progeny of trisomics include diploids, parentaltype trisomics, and embryos with new chromosome anomalies. Morphology and chromosome anomalies of the embryos are compared. A possible explanation for the secondarily acquired anomalies are discussed.     

TRISOMICS IN SOLANUM CHACOENSE: FERTILITY AND CYTOLOGY

Twenty trisomic plants found in the progeny 3x x 2x crosses in Solatium chacoense and their F₁ trisomies obtained by 2x + 1 X 2x crosses were studied with respect to their fertility and cytology. The female transmission of the extra chromosome in the trisomics varied from 2 to 60 %. The transmission frequencies of F₁ trisomies were similar to their parent trisomies in most of the lines. The transmission through the pollen ranged from 0 to 20 %. Female and male fertility of the parent trisomies was high. They produced an average of 37 seeds per pollination as the female or as the male parent. The F₁ trisomies produced about half the seed set of their parent trisomies. The extra chromosomes of six trisomies were identified by pachytene analysis. They were isochromosomes for the long arms of chromosomes I, IV and IX and the short arms of IV, IX and XII. Chromosome morphology of the extra chromosomes in pachytene stage was described. A chromosome association of 12 II + 1 I was found in 66 % of the cells at MI. About 29 % of the cells had one trivalent and 5 % had three or five univalents. The frequency of trivalent formation was not affected by the length of the extra chromosome. The possibility of univalent shift in secondary trisomies was discussed.     

Spatial organization of chromosome territories in the interphase nucleus of trisomy 21 cells

In the interphase cell nucleus, chromosomes adopt a conserved and non-random arrangement in subnuclear domains called chromosome territories (CTs). Whereas chromosome translocation can affect CT organization in tumor cell nuclei, little is known about how aneuploidies can impact CT organization. Here, we performed 3D-FISH on control and trisomic 21 nuclei to track the patterning of chromosome territories, focusing on the radial distribution of trisomic HSA21 as well as 11 disomic chromosomes. We have established an experimental design based on cultured chorionic villus cells which keep their original mesenchymal features including a characteristic ellipsoid nuclear morphology and a radial CT distribution that correlates with chromosome size. Our study suggests that in trisomy 21 nuclei, the extra HSA21 induces a shift of HSA1 and HSA3 CTs out toward a more peripheral position in nuclear space and a higher compaction of HSA1 and HSA17 CTs. We posit that the presence of a supernumerary chromosome 21 alters chromosome compaction and results in displacement of other chromosome territories from their usual nuclear position.     

Cytogenetics of a new type of barley with 16 chromosomes

In the progeny of a trisomic type for chromosome 6, Purple, a 16-chromosome type was obtained, which had a pair of new metacentric chromosome 6 in excess. The new metacentric chromosome 6 was shorter than any of the 14 chromosomes of normal barley complement and showed a heteropycnotic nature at late prophase in somatic mitosis. At metaphase I in the plants with 14+one metacentric chromosome 6 (2n=15) the chromosome configuration was exclusively 7_II+1_I indicating that the extra metacentric chromosome 6 could not associate with the normal chromosome 6. At diakinesis and metaphase I in the new 16-chromosome plants most of the sporocytes showed 8_IIor 7_II+2_I. Neither tetravalents nor trivalents were observed at meiosis. The chromosome behaviour at anaphase I and later stages of meiosis was regular in general, resulted in a fairly high pollen fertility of about 61 per cent. Seed fertility however, was very low. The transmission rate of the new metacentric chromosome 6 through the pollen was extremely low in 16-chromosome plants. Possible origin of new basic number and B-chromosome in diploid level through trisomic condition was suggested (Summary see p. 138).Contribution No. 141 of the Department of Plant Science, University of Manitoba.     

Ring chromosomes in barley (Hordeum vulgare L.)

A plant with 2n = 14 + 1 ring chromosomes was obtained in the progeny of a primary trisomie for chromosome 7 of a two-rowed cultivar, Shin Ebisu 16. The morphological characteristics of the trisomic plants with an extra ring chromosome were similar to the primary trisomic for chromosome 7 (Semierect), which suggests that it originated from this chromosome. The ring chromosomes were not completely stable in mitotic cells because of abnormal behavior. Chromosome complements varied in different plants and in different roots within a plant. Root tip cells and spikes with 2n = 14 and 14 + 2 ring chromosomes were observed on plants with 14 + 1 ring chromosomes. Breakage-fusion-bridge cycle was inferred. The ring chromosome was associated with two normal homologues forming a trivalent in 17.6% sporocytes at metaphase I. The transmission of the extra ring chromosome was 23.1% in the progeny of the plant with 14 + 1 ring chromosomes. Trivalent formation may have been much higher at early prophase stages which were difficult to analyze in barley; only 4 of 120 sporocytes analyzed showed an isolated ring at pachytene. The ring chromosome moved to one pole without separation in 24.7% of the sporocytes at AI, and divided in 27.1% sporocytes giving rise to 8-8 separation. Only 10% of the sporocytes showed bridge formation at AI.