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KARYOLOGICAL STUDIES IN SOME SPECIES OF HORDEUM

Jahan, Bushreen (1995) KARYOLOGICAL STUDIES IN SOME SPECIES OF HORDEUM. PhD thesis, University of Karachi, Karachi.

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Abstract

Somatic karyotype, distribution pattern of constitutive heterochromatin and meiotic chromosomal associations in diploid and tetraploid Hordeum species were studied by aceto-orcein/N-banding/propionic-carmine staining techniques. Detailed morphological observations of aceto-orcein stained somatic chromosomes included total length, arm ratio and presence of satrellites. The cytological technique employed in the present study gave not only good spread of chromosomes an important prerequisite for karyotype analysis, but was also reliable and reproducible. N-banding patterns in wild species of Hordeum were described for the first time. An ideogram was developed for each studied species/taxa of Hordeum for the description of individual N-bands. The banding patterns especially the finer intercalary and distal bands were more easily observed and reliably scored in late prophase and early metaphases when the chromosomes are at the right stage of contraction. Polymorphism in banding patterns in Hordeum species/taxa revealed that there was considerable band polymorphism and practically all the plants studied were unique in their banding patterns. The smaller intercalary and distal bands are the most variablein occurrence while the bands adjacent to the centromere vary in size. Banding pattern similarity together with duplication both within and between speices, seem to preclude their use as outright specific markers. Identification of somatic chromosomes and their banding pattern polymorphism in several taxa of Hordeum vulgare was studied by Giemsa N-banding technique. Chromosomes were numbered according to the wheat homoeologue groups. Every chromosome of barley possessed a different degree of constitutive heterochromatin that facilitates identification of chromosome I through 4, which almost impossible to identify by conventional staining techniques. However a wide variation in the intensities of bands, number of bands and their position in the chromosomes had been found. The classification of the bands was in accordance to Generalized Cytological Nomenclature of Cereal Chromosomes (GCNCC). In designating a particular band five items, the chromosome number, the genome desganation the arm symbol (‘S’ for short and ‘L’ for long arm), the region number and the band number were used. The band number had been separated from the region number and the band number were used. The band number had been separated from the region number by a decimal point. Thus for most arms, bands could be counted consecutively from the centromere extremities. Dark and light bands represent heterochromatic and euchromatic regions respectively. Only darkly stained (heterochromatic) reproducible N-bands had been considered as lnd mark which were diagnostic in the identification of individual chromosomes. They also sub divide each arm into easily recognizable light stained (euchromatic) bands. Many other faint N-bands were indicated by hatched lines. The majority of bands recoganized in all varieties were contromeric or interstitial. Band polymorphism was observed on all chromosomes. Chromosome 1H, exhibited typical banding pattern in all taxa except ssp. Spntaneum. In spite of the polymorphism, the similarity in the banding patterns of H. agriocrighon and H. spontaneum to that of H. vulgare suggesting their conspecificity. Meiotic pairing was studied in several taxa belonging to six species of Hordeum. The diploid taxa showed regular formation of seven bivalents. Sometimes univalent (0.6/cell), trivalents (0.12/cell) and quadrivalents (0.04/cell) were also found in H. chilense. Tetraploid species showed the occurrence of fourteen bivalents. Regular formation of bivalents in tetraploid speices suggests its allopolyploid origin. All the investigated taxa of Hordeum had fairly high frequencies of ring bivalents. Furthermore, the frequencies of ring and rod bivalents in different accdessions of the same species were not necessarily consitent. Chiasma frequency per cell at metaphase-I varied from 14.14 to 20.08 in diploid and from 34.04 to 36.04 in tetraploid species. Chiasma frequency of different Hordeum species in the present study revealed that tetraploid species had almost double the number of chiasmata per pollen mother cell than diploids. Constancy in average chiasma frequency per bivalent both for diploids and tetraploids, indicating a strong genetic control of the distribution of chiasma number within the genome

Item Type:Thesis (PhD)
Uncontrolled Keywords:hordeum species, somatic karyotype, diploid, teteraploid, karyological studies
Subjects:Biological & Medical Sciences (c) > Biological Sciences(c1) > Paleo-botany(c1.9)
ID Code:980
Deposited By:Mr. Muhammad Asif
Deposited On:23 Nov 2006
Last Modified:04 Oct 2007 21:03

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