Desynapsis and spindle abnormalities leading to 2n pollen formation in Vaccinium darrowi

Cytological investigation revealed desynapsis in microsporogenesis of a wild diploid clone of Vaccinium darrowi. Expression of desynapsis appears variable among the pollen mother cells (PMCs). In the PMCs expressing desynapsis, all or most chromosomes appeared to be completely desynapsed before anaphase I (AI) since bivalents were rare at this stage. In some PMCs complete separation of chromatids was also observed before AI. Consequently, one or both meiotic divisions were lacking, which in turn suggests either a lack of spindle formation or function. Lack of spindle function was hypothesized from the observation that in PMCs with only separated chromatids (daughter chromosomes) before AI or anaphase II (AII), their subsequent movement to anaphase poles was not observed. Thus, spindle formation or function appears to be dependent on paired homologues (bivalents) or minimally joined sister chromatids (univalents) being present. Omission of meiosis II could lead to formation of fertile 2n pollen (~5%), since a balanced chromosome complement would be expected with an equational division of the entire chromosome complement at AI. The genetic constitution of the 2n gamete would be equivalent to first division restitution (FDR) origin. If chiasmata are lacking then recombination would be absent, and 100% transmission of parental heterozygosity would be expected with FDR 2n gametes. Because desynapsis may arise from the lack of effective chiasmata between the paired homologues, a high level of parental heterozygosity is expected to be retained in the 2n gametes. The potential usage of the 2n gametes in blueberry breeding was discussed.Key words: desynapsis, spindle abnormality, 2n pollen, blueberry.

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CYTOLOGY OF 2n POLLEN FORMATION IN DIPLOID ALFALFA, MEDICAGO SATIVA

Canadian Journal of Genetics and Cytology ◽

10.1139/g79-057 ◽

1979 ◽

Vol 21 (4) ◽

pp. 525-530 ◽

Cited By ~ 52

Author(s):

Nicholi Vorsa ◽

E. T. Bingham

Keyword(s):

Medicago Sativa ◽

Seed Set ◽

Pollen Grains ◽

Genetic Constitution ◽

2N Pollen ◽

Diploid Parent ◽

2N Gamete ◽

Medicago Sativa L ◽

Pollen Formation ◽

Mother Cells

Four diploid (2x) clones of alfalfa, Medicago sativa L., which produced good seed set when used as male parents in 4x-2x crosses were selected for study. The 2x clones descended from 2x haploids of cultivated 4x alfalfa. Fertility in the 4x-2x cross was due to the production of pollen with the unreduced chromosome number (2n pollen) from the 2x parent. The cytological mechanism of 2n pollen formation was found to be disorientation of spindles at metaphase II in up to 38% of the pollen mother cells. Thus, both n and 2n pollen were produced by all four diploids examined. Normal spindles at metaphase II were oriented such that they defined the poles of a tetrahedron and resulted in normal tetrads in a tetrahedral arrangement. Disoriented spindles were basically parallel to each other and resulted in formation of dyads and occasionally a triad. Dyads developed into two 2n pollen grains; triads developed into one 2n and two n pollen grains. Since both n and 2n pollen grains are produced by the diploids, they can be maintained as diploids or they can be used as male parents in crosses to tetraploids. The genetic constitution of 2n pollen resulting from parallel spindles is similar to that expected after first division restitution of meiosis and much of the heterozygosity of the diploid parent is conserved in the gametes. The 2n gamete mechanism has potential application in germplasm transfer and in maximizing heterozygosity in tetraploid hybrids.

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Homoeologous recombination in 2n-gametes producing interspecific hybrids of Lilium (Liliaceae) studied by genomic in situ hybridization (GISH)

Genome ◽

10.1139/g98-167 ◽

1999 ◽

Vol 42 (4) ◽

pp. 681-686 ◽

Cited By ~ 27

Author(s):

G I Karlov ◽

L I Khrustaleva ◽

K B Lim ◽

J M van Tuyl

Keyword(s):

In Situ Hybridization ◽

Interspecific Hybridization ◽

2N Gametes ◽

Lilium Longiflorum ◽

Genomic In Situ Hybridization ◽

2N Pollen ◽

Rdna Sites ◽

Clear Differentiation ◽

Pollen Formation

Interspecific hybridization of Lilium longiflorum (L) with Asiatic (A) lily hybrids results in so-called LA-hybrids. Some of these hybrids produce 2n-pollen, which were used to perform crosses on Asiatic and Oriental (O) hybrids, resulting in ALA- and OLA-hybrids. Recombination between homoeologous chromosomes (introgression) and the mechanism of 2n-pollen formation in these hybrids were studied using genomic in situ hybridization (GISH). A clear differentiation between the chromosomes of L. longiflorum, Asiatic, and Oriental hybrids was observed in four ALA- and one OLA-hybrid using GISH. Two ALA-hybrids showed 3 and 5 recombinant chromosomes with a total of 5 and 10 crossover sites per hybrid, respectively. These occurred at random positions on the chromosomes. The number and the location of the rDNA-sites were determined using in situ hybridization and provided a tool, the FISH-marker, for identifying the NOR-bearing chromosomes in the lily hybrids. Evidence for the occurrence of the FDR-mechanism (first division restitution) of 2n-pollen formation in the LA-hybrids was obtained on the basis of absence of homologous chromosomes of L. longiflorum in the ALA- and OLA-hybrids.Key words: Lilium longiflorum, introgression, FDR, interspecific hybridization, FISH.

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Cytology of 2n Pollen Formation in Diploid Crested Wheatgrass, Agropyron cristatum

Crop Science ◽

10.2135/cropsci1992.0011183x003200060011x ◽

1992 ◽

Vol 32 (6) ◽

pp. 1361-1365 ◽

Cited By ~ 7

Author(s):

Ian M. Ray ◽

Mary K. Tokach

Keyword(s):

Agropyron Cristatum ◽

2N Pollen ◽

Crested Wheatgrass ◽

Pollen Formation

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NONSTRUCTURAL CHROMOSOME DIFFERENTIATION AMONG WHEAT CULTIVARS, WITH SPECIAL REFERENCE TO DIFFERENTIATION OF CHROMOSOMES IN RELATED SPECIES

Genetics ◽

10.1093/genetics/97.2.391 ◽

1981 ◽

Vol 97 (2) ◽

pp. 391-414

Author(s):

Jan Dvořák ◽

Patrick E McGuire

Keyword(s):

Chinese Spring ◽

Structural Changes ◽

Wheat Cultivar ◽

Chromosome Complement ◽

Triticum Aestivum L ◽

Substitution Lines ◽

Structural Differentiation ◽

Chromosome Differentiation ◽

Mother Cells ◽

Homoeologous Chromosomes

ABSTRACT Wheat cultivar Chinese Spring (Triticum aestivum L. em. Thell.) was crossed with cultivars Hope, Cheyenne and Timstein. In all three hybrids, the frequencies of pollen mother cells (PMCs) with univalents at metaphase I (MI) were higher than those in the parental cultivars. No multivalents were observed in the hybrids, indicating that the cultivars do not differ by translocations. Thirty-one Chinese Spring telosomic lines were then crossed with substitution lines in which single chromosomes of the three cultivars were substituted for their Chinese Spring homologues. The telosomic lines were also crossed with Chinese Spring. Data were collected on the frequencies (% of PMCs) of pairing of the telesomes with their homologues at MI and the regularity of pairing of the remaining 20 pairs of Chinese Spring chromosomes in the monotelodisomics obtained from these crosses. The reduced MI pairing in the intercultivar hybrids was caused primarily by chromosome differentiation, rather than by specific genes. Because the differentiation involved a large part of the chromosome complement in each hybrid, it was concluded that it could not be caused by structural changes such as inversions or translocations. In each case, the differentiation appeared to be unevenly distributed among the three wheat genomes. It is proposed that the same kind of differentiation, although of greater magnitude, differentiates homoeologous chromosomes and is responsible, together with structural differentiation, for poor chromosome pairing in interspecific hybrids.

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B chromosome in Plantago lagopus Linnaeus, 1753 shows preferential transmission and accumulation through unusual processes

Comparative Cytogenetics ◽

10.3897/compcytogen.11i2.11142 ◽

2017 ◽

Vol 11 (2) ◽

pp. 375-392 ◽

Cited By ~ 1

Author(s):

Manoj K. Dhar ◽

Gurmeet Kour ◽

Sanjana Kaul

Keyword(s):

B Chromosome ◽

Unreduced Gametes ◽

Molecular Techniques ◽

Root Tip ◽

Genetic Constitution ◽

Preferential Transmission ◽

Female Sex ◽

Process Formation ◽

Plantago Lagopus ◽

Mother Cells

Plantagolagopus is a diploid (2n = 2x =12) weed belonging to family Plantaginaceae. We reported a novel B chromosome in this species composed of 5S and 45S ribosomal DNA and other repetitive elements. In the present work, presence of B chromosome(s) was confirmed through FISH on root tip and pollen mother cells. Several experiments were done to determine the transmission of B chromosome through male and female sex tracks. Progenies derived from the reciprocal crosses between plants with (1B) and without (0B) B chromosomes were studied. The frequency of B chromosome bearing plants was significantly higher than expected, in the progeny of 1B female × 0B male. Thus, the B chromosome seems to have preferential transmission through the female sex track, which may be due to meiotic drive. One of the most intriguing aspects of the present study was the recovery of plants having more chromosomes than the standard complement of 12 chromosomes. Such plants were isolated from the progenies of B chromosome carrying plants. The origin of these plants can be explained on the basis of a two step process; formation of unreduced gametes in 1B plants and fusion of unreduced gametes with the normal gametes or other unreduced gametes. Several molecular techniques were used which unequivocally confirmed similar genetic constitution of 1B (parent) and plants with higher number of chromosomes.

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