The origin of natural tetraploid loach Misgurnus anguillicaudatus (Teleostei: Cobitidae) inferred from meiotic chromosome configurations

In the loach, or Oriental weatherfish Misgurnus anguillicaudatus (Teleostei: Cobitidae), diploid (2n = 50) and tetraploid individuals (4n = 100) are often sympatric in central China. The evolutionary mechanism of this tetraploidization was analyzed with the observation of meiotic behavior of chromosomes in both the germinal vesicles of mature oocytes and the primary spermatocytes in diploid and tetraploid loaches. Whereas diploid specimens usually showed 25 bivalents in meiotic cells, tetraploid loaches exhibited 0-6 quadrivalents and 38-50 bivalents in both sexes, with the modal number of quadrivalents as three in females and four in males. In the diploid specimens, the two largest metacentric chromosomes bearing nucleolar organizing regions (NORs) identified by chromomycin A(3) staining and fluorescence in situ hybridization with a 5.8S + 28S rDNA probe formed one bivalent with terminal association. In the tetraploids, four NOR-bearing chromosomes never formed a quadrivalent, but were organized into two terminally-associated bivalents. These findings suggest an autotetraploid origin of the natural tetraploid loach and subsequent rediploidization of whole genome. The latter process, however, seems still in progress as inferred from the concurrence of up-to several quadrivalents and the majority of bivalents.     

Pairing of ZW gonosomes and the localized recombination nodule in two Z-autosome translocations in Gallus domesticus

Electron microscopic observations of synaptonemal complexes of oocytes from chickens heterozygous for two Z-autosome translocations have been used to identify and study the pairing region of the Z and W chromosomes. The two translocations, MN t(Z;1) and t(OH 10), have breakpoints in opposite arms of the Z, and the arm having the breakpoint of MN t(Z;1) is marked by the terminal C+ band. In both translocations the short arm of the W was specifically paired with the euchromatic short arm of the Z. In MN t(Z;1) only open quadrivalents (74%) and trivalents plus W univalents (26%) were observed, whereas t(OH 10) exhibited, in addition to the prevalent quadrivalents (62%), III + I (19%) and II + II (19%) configurations. The extent of W pairing was slightly decreased in MN t(Z;1) (68.4% of the W chromosomes paired) and considerably decreased in t(OH 10) (25.3% of the W chromosomes paired). Nonhomologous synapsis occurred regularly at the quadrivalent crosspoint in MN t(Z;1) and also in bivalents from t(OH 10). The recombination nodule normally located in the terminus of the pairing region in normal ZW pairs is present in both translocations without any alteration of its frequency or its strict terminal position. Based on these data and previous observations (Rahn and Solari, 1986), it is proposed that an obligatory recombination event occurs at a locus between 0.7 microns and 0.15 microns of the paired ZW telomeres, establishing a recombinational region and a pseudoautosomal region which determine partial sex-linkage and no sex-linkage, respectively. Most of the pairing region of the ZW pair is nonhomologously paired.     

Synaptonemal complex analysis of X-7 translocations in male mice

The synaptonemal complexes of surface-spread spermatocytes of mice heterozygous for one of two reciprocal translations (R3 and R5) between the X and chromosome 7 have been examined by light and electron microscopy (EM). The break points of R3 were determined to be at 70% of chromosome 7, as measured from the centromere, and at 22% of the X. Translocation quadrivalents were formed almost exclusively. The break points of R5 were at 21% of chromosome 7 as measured from the centromere, and at 83% of the X. There was little indication that the break in the X interfered with sex-chromosome synapsis between the 7X and Y. Univalent Y's were not observed in R3, and only seldom observed (8–14%) in R5. However, in contrast to R3, R5 formed quadrivalents relatively rarely (20% in the EM study of 100 nuclei), and heteromorphic bivalents of 7X-Y and X7-7 quite frequently (72%). Possible causes of this high bivalent frequency are discussed. Light-microscope (LM) analysis alone was found to be inadequate for interpreting synaptic configurations (quadrivalents vs. bivalents) in R5. The LM analysis was further complicated by the occurrence of nonhomologous synapsis in the heteromorphic bivalents of R5, a phenomenon easily recognized and interpreted in the EM portion of the study.     

Meiosis in triploid Lolium. I. Synaptonemal complex formation and chromosome configurations at metaphase I in aneuploid autotriploid L. multiflorum.

A spreading technique for synaptonemal complexes (SCs) was applied to pollen mother cells of two aneuploid genotypes of autotriploid Lolium multiflorum (2n = 3x + 1 = 22). In the earliest nuclei analyzed the axial elements are in six groups of 3 and one group of 4. Most groups have formed multivalents with from one to five pairing partner exchanges, but there are also groups that have formed bivalents and univalents. Some axial elements have formed triple associations, in one case for the length of the trivalent. Unsynapsed axial elements remain aligned with their homologous SCs into pachytene, but this alignment is abolished as these axes pair heterologously among themselves until the entire axial element complement is synapsed. At metaphase I most chromosomes are associated as trivalents and quadrivalents.     

Synaptonemal complex analysis of X-7 translocations in male mice: R2 and R6 quadrivalents

Synaptonemal complexes of surface-spread spermatocytes of mice heterozygous for reciprocal translocations R2 or R6 between the X-chromosome and chromosome 7 were examined by light and electron microscopy (EM). Measurements of the lengths of all chromosome axes involved in the translocation configurations and of the extent of synapsis were used to calculate the position of the break points of the two translocations. The breaks for R2 were determined to be at 62% of the 7 as measured from the centromere, and at 27% of the X. Quadrivalents were formed almost exclusively. The break points for R6 were calculated to be at 30% of the 7 as measured from the centromere, and at 75% of the X. Although in R6 the break in the X lies within the potential pairing region of the sex chromosomes, univalent Ys were rarely observed (6%). The EM sample of 76 nuclei contained: 42% quadrivalents, 52% heteromorphic bivalents, 4% trivalent plus Y univalent, and 2% X7-7 bivalent plus two univalents (7X and Y). Nonhomologous synapsis occurred in the quadrivalents of both R2 and R6. In R6 nonhomologous synapsis of the X portion of the 7X with the 7 involved up to 14% of the length of the 7. Methods are discussed for determining the position of the break points in the presence of nonhomologous synapsis. It is proposed that the high percentage of bivalents is due to premature desynapsis of the 7X from the 7 and that the X portion of the 7X axis confers its property of premature desynapsis on that portion of the 7 to which it is attached.     

Autosyndetic pairing in Gibasis (Commelinaceae) hybrids revealed by C-banding

Two closely related species of Gibasis, G. karwinskyana and G. consobrina, and their F₁ hybrids were studied cytologically at the diploid and tetraploid level. Despite similarity in their basic karyotype, pairing was extremely limited in the diploid hybrid and almost exclusively autosyndetic in the tetraploid, except for multivalent formation due to interchange heterozygosity. The analysis was considerably facilitated by the use of C-banding techniques at meiosis, by which the chromosomes of each species could be readily identified. In the parents, quadrivalents were formed between homologous but non-identical chromosomes, which also formed autosyndetic bivalents in the hybrids. Meiotic pairing in the hybrids was unaffected by polytypy for C-bands among different populations of the parental species.     

Synaptonemal complexes in a tetraploid mouse spermatocyte

Quadrivalents, represented by unique synaptonemal complex configurations, together with normal bivalents are observed for the first time in a mammalian tetraploid pachytene spermatocyte prepared by microspreading. The chromosomal axes (lateral elements) clearly demonstrate the switching of partners in the quadrivalents as predicted from classical cytogenetic theory. Tetraploid formation, possibly by nuclear fusion, must have occurred prior to meiotic prophase.     

芜菁的诱导同源四倍体减数分裂分析

细胞学上芜菁 (Brassicarapa)为正常的二倍体 ,具有 1 1的联会和 1 - 1的染色体分离。它的花粉母细胞 (PMC’s )在小孢子发生过程中的减数分裂前期 (M1 )无“B染色体” ,也无任何次级缔合。用 0 0 2 %的秋水仙碱水溶液处理 6h对多倍体的诱导形成明显。诱导出的同源四倍体构型中无联会基因 ,而成 1或 2次交叉的二价体、三价体和四价体。从多倍体逆转的有趣现象中发现 ,4 6 7%的诱导多倍体后来恢复成二倍体。不平衡的染色体分离普遍存在于诱导出的同源四倍体中 ,这就是导致生存能力不同的异常配子体出现的主要原因。异常配子体的结合 ,在芸苔属 (Brassica)现存种的演化中起到了重要作用     

四倍体高粱与约翰逊草间的亲缘关系分析

本研究以四倍体高粱与约翰逊草为材料,利用SSR分子标记和细胞遗传学方法分析了高粱与约翰逊草间的亲缘关系,SSR分析结果表明,高粱与约翰逊草的遗传背景差异较大,SSR差异位点和相似位点在连锁群上的分布具不平衡性;按照差异引物出现频率高低,将连锁群分为两类：高度差异区和低度差异区。细胞学分析结果表明：（1）双亲及杂交种都是不规则的四倍体遗传群体。（2）花粉母细胞减数分裂中期I,双亲及杂交种染色体配对以二价体和四价体为主,杂交种平均每个细胞二价体数为17．00,四倍体高粱为15．23、约翰逊草为15．83,四价体数分别为0．95,2．15和1．60个。但杂交种减数分裂过程中也出现一定数量的单价体,减数分裂会形成一定比例的非整倍配子。SSR检测结果与细胞学分析结果具有一致性,约翰逊草与高粱的染色体组间存在一定程度的同源性。二者杂交不能形成稳定遗传的双二倍体。     

Chromosome differentiation in diploid species of Lotus (Leguminosae)

Summary Meiotic chromosome behavior was studied in seven diploid species of Lotus (L. alpinus Schleich., L. japonicus (Regel) Larsen, L. filicaulis Dur., L. schoelleri Schweinf., L. krylovii Schischk. and Serg., L. tenuis Waldst. et Kit., L. corniculatus var. minor Baker) and in 51 interspecific hybrids from 16 different crosses. Meiosis in the diploid species was quite regular. In a high proportion of the PMC's of the hybrids there was close chromosome homology with a normal association of 6 II's. However, meiotic irregularities including bridges, lagging chromosomes, univalents, and quadrivalents, occurred in a small percentage of the cells. The late separation of bivalents, the presence of quadrivalents, and inversion bridges with fragments, would indicate for some hybrids that certain chromosomes were structurally differentiated. The large number of rod bivalents observed at diakinesis was also highly suggestive that genetic nonhomology in one chromosome arm could contribute to the frequency of this type of bivalent. Therefore, the maximum number of 6 II's which occurred in a high percentage of cells may be misleading in that cryptic structural differences between chromosome arms, or segments, are not revealed. Pollen fertility in the species and hybrids was not correlated with meiotic irregularities suggesting that pollen fertility is genotypically controlled.     

Quantitative analysis of diploid translocation heterozygotes: test of models and equations

Summary Equations have been derived for two different models of chromosome pairing and chiasmata distribution. The first model represents the normal condition and assumes complete synapsis of homologous bivalents and the arms of interchange quadrivalents. This is followed by a nonrandom distribution of chiasmata among bivalents and multivalents such that each bivalent or bivalent-equivalent always has at least one chiasma. Univalents occur only as part of a III, I configuration at diakinesis or metaphase I. The second model assumes that a hologenomic mutation is present in which all chromosomes of a genome are equally affected. Two different assumptions can be made for such a mutation, and both give the same results: (1) homologous or homoeologous chromosome arms may be randomly paired or unpaired, but synapsis always leads to a crossover; (2) homologous or homoeologous arms always pair, but chiasmata are randomly distributed among the arms. The meiotic configurations at diakinesis or metaphase I are the same for both assumptions. Meiotic configurations of normal diploid interchange heterozygotes show good agreement with numbers predicted by the equations for nonrandom chiasmata distribution among configurations. Inter-specific hybrids with supernumerary chromosomes produced meiotic configurations frequencies in agreement with predictions of equations for random chiasmata distribution, but a hybrid without supernumeraries fitted the nonrandom expectations.     

Pachytene pairing and oocyte numbers in mice with two single Robertsonian translocations and the male-sterile compound with monobrachial homology

Oocyte numbers and synaptonemal complexes were studied in two Robertsonian translocations, Rb(6.15)1Ald and Rb(4.6)2Bnr, and their male-sterile compound. Oocyte numbers in the compound were lower than those of either parent, and there was a marked difference between reciprocal crosses. Synaptonemal complexes of homozygous females appeared as 19 bivalents, those of single heterozygotes as 18 bivalents and a trivalent, and those of compound heterozygotes as 17 bivalents and a quadrivalent. Most trivalents were fully paired, whereas the majority of quadrivalents exhibited terminal asynapsis. About one-half of all oocytes had other pairing abnormalities, probably reflecting reduced survivability. Whereas all fully paired quadrivalents were present in cells not showing any pairing anomalies, one-half of the quadrivalents with terminal asynapsis were seen in oocytes with other anomalies. It is suggested that in oocytes destined for atresia, there is a predisposition to synaptic failure of translocation configurations. Additional oocytes are likely to break down because of the deleterious effect of the compound translocation on gametogenesis. This effect seems to be more pronounced in Rb1Ald/Rb2Bnr spermatocytes than in oocytes.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

Meiotic cytology of Saccharomyces cerevisiae in protoplast lysates

Summary This report describes cytological features of meiosis in Saccharomyces cerevisiae prepared for electron microscopy by lysis of protoplasts or nuclei on an aqueous surface. Whereas the chromatin of cells lysed before or after meiotic prophase was widely dispersed, pachytene bivalents appeared as discrete, elongate masses of compact chromatin. These bivalents were of nearly uniform thickness; they ranged in length from about 0.6 m to 4.0 m, with a median of 1.6–1.8 m. Enzymatic digestion of chromosomal DNA removed the chromatin to reveal the underlying synaptonemal complex. The lysis of partially purified nuclei was less disruptive and thereby revealed the regular association of the telomeres with fragments of the nuclear envelope. In tetraploid cells, pachytene lysates contained quadrivalents characterized by the close apposition of chromatin masses of similar length. One or more points of intimate association appear to represent sites of exchange between pairing partners. The departure of the diploid cells from pachytene was accompanied by the renewed association of spindle microtubules with the chromosomes shortly before the diplotene chromosomes decondensed. Later, the successive meiotic divisions were identified by the appearance of a single spindle for meiosis I and of two spindles for meiosis II.     

四倍体鲫鲤、三倍体湘云鲫染色体减数分裂观察

用精巢细胞直接制片法观察了异源四倍体鲫鲤、三倍体湘云鲫和二倍体红鲫、湘江野鲤精母细胞染色体第一次减数分裂中期配对情况 ;作为对照 ,观察了上述四种鱼肾细胞的有丝分裂中期染色体。在精母细胞第一次减数分裂中 ,异源四倍体鲫鲤同源染色体两两配对 ,形成 10 0个二价体 ,没有观察到单价体、三价体和四价体 ;三倍体湘云鲫精母细胞形成 5 0个二价体和 5 0个单价体 ;红鲫和湘江野鲤精母细胞分别形成 5 0个二价体。肾细胞检测表明异源四倍体的染色体数目为 4n =2 0 0 ;湘云鲫为 3n =15 0 ;红鲫和湘江野鲤分别为 2n =10 0。减数分裂时染色体分布情况与肾细胞染色体检测结果相吻合。具有四套染色体的异源四倍体鲫鲤在减数分裂中只形成 10 0个二价体 ,而不形成 2 5个四价体或其它形式 ,为产生稳定一致的二倍体配子提供了重要的遗传保障 ,也为人工培育的异源四倍体鲫鲤群体能够世世代代自身繁衍下去提供了重要的遗传学证据。三倍体湘云鲫在减数分裂过程中出现二价体、单价体共存 ,同源染色体在配对和分离中出现紊乱 ,导致非整倍体生殖细胞的产生 ,为湘云鲫的不育性提供了染色体水平上的证据     

Production and meiotic analysis of autotriploid Triticum speltoides and T. bicorne

Summary Autotriploid Triticum speltoides and T. bicorne (2n=3x=21) were produced by pollinating autotetraploids with pollen from their respective diploids. The autotriploid plants were vigorous, male sterile, and morphologically resembled their diploid parents. At meiosis, T. speltoides (3x) averaged 2.52 univalents, 0.42 rod bivalents, 2.03 ring bivalents, 4.48 trivalents, and 0.03 chain quadrivalents per cell, and T. bicorne (3x) had 2.30 univalents, 0.20 rod bivalents, 2.10 ring bivalents, and 4.70 trivalents. Panhandle trivalents made up 27% of the total trivalents, and involved 18% of the total number of chromosomes observed in T. bicorne (3x), and 26% and 17% in T. speltoides (3x), respectively. The observed chromosome pairing in both triploids was predicted well from the expressions developed by Alonso and Kimber.Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 10932     

Tissue-culture-facilitated production of aneupolyhaploid Thinopyrum ponticum and amphidiploid Hordeum violaceum x H. bogdanii and their uses in phylogenetic studies

Summary An aneupolyhaploid (2n = 36) of the decaploid Thinopyrum ponticum and an amphidiploid (2n = 28) of Hordeum violaceum x Hordeum bogdanii were produced through anther and inflorescence culture, respectively. Meiotic associations in pollen mother cells at metaphase I of these plants were analyzed. The aneupolyhaploid arose by direct embryogenesis from a microspore without passing through a callus phase. The mean pairing frequencies of 2.67 univalents ⁺ 0.54 rod bivalents ⁺ 8.85 ring bivalents ⁺ 2.75 trivalents ⁺ 0.17 chain quadrivalents ⁺ 0.56 ring quadrivalents ⁺ 0.65 pentavalents in the aneupolyhaploid (2n = 36) best fit the 221 model. However, the frequent multivalents (up to five trivalents, or three quadrivalents, or four pentavalents in a cell) indicated that decaploid T. ponticum has five sets of closely related genomes representable by the genome formula J₁ J₁ J₁ J₂ J₂. Colchicine treatment of inflorescence-derived H. violaceum x H. bogdanii regenerants greatly enhanced the rate of chromosome doubling, and completely doubled regenerants could be isolated. The H. violaceum x H. bogdanii amphidiploid had a mean pairing pattern of 12.53 univalents ⁺ 5.57 rod bivalents ⁺ 1.97 ring bivalents ⁺ 0.07 trivalents ⁺ 0.03 hexavalents, indicating the presence of desynaptic gene(s) in the original diploiid hybrid. Therefore, the pairing frequency in that diploid hybrid was an under-estimate of chromosome homology between the parental genomes, and additional diploid hybrids are needed to assess the genome homology between H. violaceum and H. bogdanii. These two contrasting experiments demonstrated that tissue culture techniques are useful in altering the ploidy level to produce plant materials suitable for genome analysis and phylogenetic studies.Cooperative investigation of the USDA-ARS, Forage and Range Research Laboratory, Logan, UT 84322-6300, and the Utah Agricultural Experiment Station, Utah State University, Logan, UT 84322-4810. Approved as journal paper No. 3991     

Pachytene pairing in relation to sperm and oocyte numbers in a male-fertile reciprocal translocation in the mouse

In adult males carrying the male-fertile reciprocal translocation T(2;4)13H, body weights, testis weights, and sperm counts were higher in heterozygotes than in homozygotes. Heterozygotes whose mothers were C3H/He exceeded their reciprocal counterparts in the same criteria. At 3-4 days of age, no significant differences between homozygous and heterozygous females were found in body weight, ovarian volume, or oocyte numbers, although mean oocyte volumes were somewhat larger in heterozygotes than in homozygotes. In homozygous males and females the synaptonemal complexes of rearranged chromosomes appeared as bivalents that were indistinguishable from normal bivalents. In most gametocytes of heterozygotes, the translocation was present in the form of a quadrivalent. The degree of pairing failure was greater in oocytes than in spermatocytes. Terminal asynapsis of quadrivalents was very rare in spermatocytes, but it affected one quarter of the oocytes. Only very few translocation configurations were associated with the XY bivalent. It is concluded that the number of sperm produced in male heterozygotes can match the general increase in vigor by the formation of a high level of fully paired quadrivalents, whereas a greater degree of terminal asynapsis in the quadrivalents of oocytes may indicate a slightly more deleterious effect of this translocation on oogenesis.     

Pachytene pairing and metaphase I configurations in a tetraploid somatic Lycopersicon esculentum x L. peruvianum hybrid.

In the tetraploid somatic hybrid between the diploid Lycopersicon species L. esculentum (tomato) and L. peruvianum, synaptonemal complexes formed quadrivalents in 73 of the 120 sets of four chromosomes (60.8%) in 10 cells studied in detail at pachytene. Of these, 43 had one pairing partner exchange, 22 had two, and 8 had three, very close to a Poisson distribution. The points of pairing partner exchange were concentrated at the middle of the two arms. The frequency per arm corresponded with physical arm length. There was a sharp drop around the centromere, and pericentric heterochromatin had a slightly lower probability of being involved in pairing partner exchange than euchromatin. The chromosomes align before pairing and there are several points of pairing initiation, with concentrations at or near the ends and the centromere. From zygotene to late pachytene the quadrivalent frequency decreased considerably. At late pachytene it was lower than expected with the observed high frequency of pairing partner exchange. Pairing affinity between species was only slightly lower than affinity within species, in spite of considerable genetic differentiation. The frequency of recombination nodules increased from early to late zygotene and then decreased strongly to full pachytene. There is a highly significant negative correlation between percent pairing and SC length. At metaphase I the frequency of quadrivalents was 0.444, and branched quadrivalents were rare, probably caused by interference and restriction of chiasma formation to distal euchromatin. Metaphase I quadrivalent frequency is a relatively good indication of pairing affinity in this material.     

CHROMOSOME ANALYSIS OF HYBRIDS BETWEEN 4N GRINDELIA CAMPORUM AND 2N G. GRANDIFLORA (COMPOSITAE)

Morphology and meiosis are described in four progeny plants resulting from tetraploid Grindelia camporum Greene (2n = 24) from California pollinated by diploid G. grandiflora Hook. (2n = 12) from Coahuila, Mexico. Three of the four progeny were tetraploid, morphologically like the pistillate parent, and had metaphase I chromosome configurations which included quadrivalents and a complementary number of bivalents. They are considered to have resulted from selfing. The fourth plant was triploid (2n = 18) andmorphologically intermediate between the parents. Chromosome configurations in the triploid were variable with univalents, ring and rod bivalents, trivalents and pentavalents. These two species are considered related through an ancestor with a basic genome, but are separated cytologically by polyploidy and by two distinct chromosomal interchanges that explain the configurations observed in the triploid hybrid.