CHROMOSOME PAIRING IN POA ANNUA L.

1973 ◽  
Vol 15 (3) ◽  
pp. 549-551 ◽  
Author(s):  
W. M. Ellis ◽  
B. T. O. Lee ◽  
D. M. Calder
Keyword(s):  
Chromosome Pairing ◽  
Breeding System ◽  
Tetraploid Plant ◽  
Poa Annua ◽  
Diploid Population ◽  
Bivalent Formation

Cytological studies carried out on six tetraploid and one diploid population and a synthesized tetraploid plant have shown regular bivalent formation at meiosis. This regularity appears to be genetically controlled in this species. Plants from all the populations behave as diploids. The implications of this regular disomic chromosome pairing on recombination, variation and the breeding system of P. annua are considered.

THE SIGNIFICANCE OF MEIOTIC CHROMOSOME PAIRING IN TETRAPLOID (2n = 28) BROMUS PUMPELLIANUS SCRIBN. SSP. DICKSONII

1972 ◽  
Vol 14 (4) ◽  
pp. 763-771 ◽  
Author(s):  
K. C. Armstrong
Keyword(s):  
Chromosome Pairing ◽  
High Frequency ◽  
Chiasma Frequency ◽  
Karyotype Analysis ◽  
Meiotic Chromosome ◽  
Low Frequency ◽  
Meiotic Chromosome Pairing ◽  
Ring Bivalents ◽  
Bivalent Formation

Bivalent formation was predominant at meiosis in B. pumpellianus ssp. dicksonii. The average in 15 plants ranged from 11.38 to 13.77 bivalents per cell. The high chiasma frequency (23.41-26.74) was a reflection of the high frequency of ring bivalents (9.48-12.42). A low frequency of quadrivalents occurred (0.06-1.22). A karyotype of this species was presented from both a highly contracted and moderately contracted cell and the differences between these two were noted. Four satellites were found, two large and two minute. There were 3-5 submedian and 5-7 median chromosomes depending on the cell studied. In addition two subterminal chromosomes were present. The meiotic and karyotype analysis suggest a deviation from an autotetraploid behaviour, but the presence of quadrivalents and similarities between pairs in the karyotype suggested closely related genomes. Alternatively it was considered that the quadrivalents could be due to translocation heterozygotes. The implications of these results were discussed in relation to the reported meiotic events in the octoploids, B. inermis and B. pumpellianus.

GENOME RELATIONSHIPS IN BROMUS ERECTUS, B. PUMPELLIANUS SSP. DICKSONII AND B. PUMPELLIANUS

1975 ◽  
Vol 17 (3) ◽  
pp. 391-394
Author(s):  
K. C. Armstrong
Keyword(s):  
Genetic Control ◽  
Chromosome Pairing ◽  
Low Frequency ◽  
Homoeologous Chromosome ◽  
Homoeologous Chromosome Pairing ◽  
Bivalent Formation ◽  
Bromus Erectus

Chromosome pairing was studied in hexaploid (2n = 42) hybrids of B. erectus (2n = 28) × B. pumpellianus (2n = 56) and B. pumpellianus ssp. dicksonii (2n = 28) × B. pumpellianus. Chromosome pairing in the B. erectus × B. pumpellianus hybrid was complete with predominantly bivalent formation and a low frequency of quadrivalents. The pairing results support the contention that B. pumpellianus is an autoalloploid with an AAAABBBB genome formula. The B. pumpellianus ssp. dicksonii × B. pumpellianus hybrid has an AAABBB genome formula. The presence of quadrivalents, hexavalents and cells containing a total number of bivalents or bivalents plus trivalents in excess of 14 indicated pairing between the A and B genomes. However, a high univalent frequency showed that the A and B genomes were homoeologous rather than homologous. Evidence for genetic control of homoeologous chromosome pairing and homoeologous differentiation between the genomes of the species is discussed.

Chromosome pairing in octoploid F1 and octoploid amphiploid hybrids between Bromus inermis and B. pumpellianus

1985 ◽  
Vol 27 (5) ◽  
pp. 538-541 ◽  
Author(s):  
K. C. Armstrong
Keyword(s):  
Chromosome Pairing ◽  
Bromus Inermis ◽  
Chromosome Differentiation ◽  
Bivalent Formation ◽  
Tetraploid Cytotypes

Chromosome pairing in the amphiploid (8x) of 4x Bromus pumpellianus ssp. dicksonii × 4x B. inermis was compared with pairing in the F1 hybrids between natural octoploid cytotypes of B. inermis and B. pumpellianus and the octoploid parents. Predominantly bivalent pairing was found in both the amphioctoploid, octoploid F1 hybrids, and octoploid parents. Bivalent formation in the amphioctoploid could be based on chromosome differentiation between the tetraploid cytotypes of B. inermis and B. pumpellianus. These results suggest that the evolution of the octoploid cytotypes of B. inermis and B. pumpellianus could have involved hybridization of the tetraploid cytotypes.Key words: Bromus, chromosome pairing, octoploid, F1 hybrid, amphiploid.

Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L.

1986 ◽  
Vol 28 (3) ◽  
pp. 330-334 ◽  
Author(s):  
T. Attia ◽  
G. Röbbelen
Keyword(s):  
Brassica Napus ◽  
Chromosome Number ◽  
Chromosome Pairing ◽  
Structural Modification ◽  
Meiotic Pairing ◽  
Chromosome Behaviour ◽  
Preferential Pairing ◽  
Brassica Napus L ◽  
Bivalent Formation ◽  
Homoeologous Chromosomes

Newly resynthesized AC amphihaploids, which were characterized by high meiotic pairing and multivalent formulation, after doubling of their chromosome number showed preferential pairing and bivalent formation in the resynthesized amphidiploid Brassica napus (AACC). However, univalents as well as multivalents were also formed indicating that their chromosome behaviour was not fully diploidized. Stabilization of chromosome pairing in newly resynthesized amphidiploids can be achieved through genetic control or structural modification of the homoeologous chromosomes. A comparison of the meiotic behaviour of spontaneous haploids of natural rapeseed with that of the newly synthesized AC amphihaploids provides some evidence that both processes may be involved in the regulation of chromosome pairing in Brassica.Key words: Brassica, amphihaploid, amphidiploid, meiosis, univalents, multivalents.

Hybrids of Hordeum californicum and 2x H. brevisubulatum s.l. with Agropyron caninum

1985 ◽  
Vol 27 (4) ◽  
pp. 380-386 ◽  
Author(s):  
P. K. Gupta ◽  
George Fedak
Keyword(s):  
Chromosome Pairing ◽  
Floral Morphology ◽  
Embryo Rescue ◽  
Intergeneric Hybrid ◽  
Bivalent Formation ◽  
The Difference ◽  
Agropyron Caninum ◽  
Hordeum Species

Two diploid Hordeum species, H. californicum (2n = 2x = 14) and H. brevisubulatum s.l. (2n = 2x = 14), were used successfully to produce hybrids with Agropyron caninum (2n = 4x = 28) through embryo rescue techniques. The floral morphology of the hybrids was intermediate between the parents in each case. Both hybrids were triploids (2n = 3x = 21), and chromosome pairing exhibited a mean of 3.86 bivalents in the hybrid with H. californicum and a mean of 5.53 bivalents in the hybrid with H. brevisubulatum. Bivalent formation was attributed to a common genome between the diploid Hordeum species and the tetraploid A. caninum. It could not be ascertained whether the difference in the two hybrids was due to a difference in the degree of homology or difference in meiotic control mechanisms.Key words: Hordeum, Agropyron, homeology, triploid, intergeneric hybrid.

Nature of chromosome pairing in SH-genome octaploids involving Elymus canadensis and E. trachycaulus: a genome dose dependent bivalentizing mechanism

Genome ◽  
1990 ◽  
Vol 33 (5) ◽  
pp. 613-618 ◽  
Author(s):  
P. S. Kumar ◽  
P. D. Walton
Keyword(s):  
Chromosome Pairing ◽  
Chromosome Doubling ◽  
Tetraploid Hybrid ◽  
Polygenic Control ◽  
A Genome ◽  
Structural Differences ◽  
Bivalent Formation ◽  
Elymus Canadensis ◽  
Tetraploid Level ◽  
Dose Dependent

In spite of regular chromosome pairing, hybrids between Elymus canadensis (Linnaeus) and E. trachycaulus (Link) Gould ex Shinners at the tetraploid level are sterile owing to structural differences between the donor genomes. However, the hybrids between these species at the octaploid level (obtained through chromosome doubling of the tetraploid hybrid and also from a cross between the octaploids of E. canadensis and E. trachycaulus) exhibited a predominance of bivalents in meiosis in spite of the autotetraploid nature of their constituent S and H genomes. The colchicine-induced amphiploids showed varying degrees of fertility. Comparison of chromosome pairing in the hybrid octaploids with that in the parental octaploids and hexaploids revealed that random bivalent formation is promoted when the S and (or) H genomes are at the tetraploid level, but not when they are in the triploid state. A bivalentizing mechanism under polygenic control is suggested to explain the predominance of bivalents in the tetraploid S and H genomes.Key words: Elymus, S genome, H genome, octaploids, bivalents, bivalentization.

Polyploidy and apomixis in the Casuarina distyla species group

1959 ◽  
Vol 7 (3) ◽  
pp. 238 ◽  
Author(s):  
BA Barlow
Keyword(s):  
Breeding System ◽  
Related Species ◽  
Genetic System ◽  
Species Group ◽  
The Other ◽  
Diploid Population ◽  
Closely Related Species ◽  
Triploid Plant

In the Casuarina distyla species group, which includes 13 closely related species, sexual tetraploid forms have been recorded in nine species and apomictic triploids in four. These forms are probably autopolyploids. The triploid apomiots are presumably diplosporous and parthenogenetic, and in two species are pseudogamous, but not in the other two. It is suggested that a transition from the former to the latter breeding system would follow elimination of the need for pseudogamy. A hypothesis is presented that polyploidy and apomixis have arisen together within the species through establishment in a diploid population of a triploid plant which is diplosporous and parthenogenetic. The genetic system involved probably spread through the group during the evolution of the species, giving them a potential for this kind of development.

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