The nature and behaviour of B chromosomes in Allium stracheyii and Urginea indica have been studied in detail. In A. stracheyii, a correlated analysis of their behaviour in root cells, pollen mother cells and pollen grains has been carried out. The presence of defective but functioning centromere has been suggested. The heterochromatic constitution of the Bs has been demonstrated. It has been shown that there is no selection barrier for the Bs to enter into the germinal line, though in the pollen grains, over and below a threshold, the B chromosomes are not favoured. The selective value of B chromosomes is exhibited by their presence in every individual of the population. As in A. stracheyii, in the U. indica as well, tetraploids are devoid of B chromosomes indicating that the adaptability conferred by Bs is not needed in tetraploids with increased tolerance range. The origin of B chromosomes has been suggested through elimination of euchromatic segments from triploids or aneuploids. © 1974, Japan Mendel Society, International Society of Cytology. All rights reserved.

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University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

CYTOLOGIA

Planta Medica

Quantitation of principal bufadienolides in different cytotypes of Urginea indica

Evidences showing that chromosomes in eukaryota, with their complex organization, exhibit dynamism in structure and behaviour for controlling differentiation, variability and reproduction have been reviewed. An outline has been given of the stepwise evolution of the functionally differentiated chromosome segments and their chemical make up including protein components and sequence complexity of DNA. The outline includes the origin of chromosomal control of metabolism in extranuclear organelles. During organogenesis, the chromosomes, maintaining the basic genetic skeleton, undergo variation in structure and chemical components, thus exhibiting dynamism. Addition, loss and inactivation of heterochromatic segments have been correlated with adaptation and alteration in chromosome size. Data on the possible role of repeated sequences in control and integration have been presented. Endomitotic replication of the chromosome, in place of normal mitosis, during differentiation is an example of dynamic behaviour, adapted to meet the need of uninterrupted transcription during differentiation without increasing the number of cells. The predetermined symmetrical growth of the organism is thus maintained. In several asexually reproducing species, dynamism is manifested in genetically controlled unusual behaviour of chromosomes, where the somatic tissue often represents a chromosome mosaic. It has been adapted to meet the need of generating variability and genotypes through bud mutation in the absence of effective sexual reproduction. Data in favour of the concept of dynamism indicate that evolution of eukaryotic chromosome has involved progressive complexity of chromosome structure on the one hand, and flexibility in its behaviour and structure, maintaining the basic genetic make up, on the other. It has enabled the chromosomes to exert supreme control on all aspects of metabolism which are sequential and phasic in higher organisms. © 1978 Indian Academy of Sciences.

Proceedings of the Indian Academy of Sciences - Section B. Part 3, Plant Sciences

Change in chromosome concept

In a population of Allium stracheyiBaker (2n=14) growing in Darjeeling both diploids and polyploids occur. The diploids contain B-chromosomes varying from 2-10 in number. Polyploids are conspicuous by absence of B-chromosomes. These in diploids are found in the pollen mother cells and also in the pollen, and some are provided with subterminal constriction. Diploid individuals when brought from Darjeeling to Calcutta (i. e. from temperate to tropical regions) became polyploid within a month and the B-chromosomes were simultaneously lost. In order to confirm this unexpected result, the transfer experiment has been repeated thrice with fresh collections in each case and selection of diploid bulbs after cytological observation. In all cases the result has been the same. In rare cases one or two B-chromosomes were found in the polyploid cells which might represent intermediate steps of the disappearance. B-chromosomes in diploids possibly help the individual to compete with polyploids by enlarging the adaptive capacity. The sudden polyploidisation by transfer from the mountains to the plains might have been the result of a shock due to the temperature difference. The high temperature may be deleterious for the reproduction of B-chromosomes, and their degeneration products possibly contribute to cytoplasmic changes and the spindle disturbances which effect polyploidisation. © 1961 Springer-Verlag.

Chromosoma

Occurrence of B-chromosomes in diploid Allium stracheyi Baker and their elimination in polyploids

Flora Mediterranea

Chromosome numbers of 9 taxa of Lilium (Liliaceae) from Turkey

The nature and behaviour of supernumerary chromosomes in the rhizirideum group of the genus Allium

Caryologia

Cytogenetics of B-Chromosomes

Nature and Behaviour of B Chromosomes in Allium Stracheyii Baker and Urginea Indica Kunth

Journal	CYTOLOGIA
Publisher	-
ISSN	0011-4545
Open Access	Yes