Chromosome banding in evolutionary plant cytogenetics
01 Feb 1983-Vol. 92, Iss: 1, pp 51-79
TL;DR: The introduction of chromosome banding techniques for linear differentiation of chromosomes have allowed the identification of the heterochromatic segments on the chromosomes, which have been utilized for inter- and intra-species comparisons and the probable phylogenetic relationships in various plant taxa from Gymnosperms, Angiosperms have been suggested.
Abstract: The introduction of chromosome banding techniques for linear differentiation of chromosomes have allowed the identification of the heterochromatic segments on the chromosomes. These heterochromatic segments are primarily composed of repetitive DNA, which are discernible in the form of dark staining regions by Giemsa C band staining or exhibit enhanced or reduced fluorescent bands by Q banding techniques depending upon the particular type of DNA repetition. The analyses of banding patterns have allowed in plants, the identification of chromosomes or parts of chromosomes, which have been utilized for inter- and intra-species comparisons. Based on the information of banding patterns, amount and distribution of heterochromatic segments, coupled with karyotypic features and morphological similarities; the probable phylogenetic relationships in various plant taxa from Gymnosperms, Angiosperms (both dicots and monocots) have been suggested. The information on heterochromatin recognition have also been utilized in suggesting probable ancestry of polyploids and the trend of evolution in varietal differentiation and speciation. Analysing the data, a probable phylogenetic significance and the direction of change in heterochromatin evolution in plants is suggested.
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01 Jan 1979
TL;DR: In this paper, Dispersed repetitive DNA sequences from yeast (Saccharomyces cerevisiae) nuclear DNA have been isolated as molecular hybrids in lambdagt and showed marked alterations in the size of the restriction fragments containing these repetitive DNAs.
Abstract: Dispersed repetitive DNA sequences from yeast (Saccharomyces cerevisiae) nuclear DNA have been isolated as molecular hybrids in lambdagt. Related S. cerevisiae strains show marked alterations in the size of the restriction fragments containing these repetitive DNAs. "Ty1" is one such family of repeated sequences in yeast and consists of a 5.6 kilobase (kb) sequence including a noninverted 0.25 kb sequence of another repetitious family, "delta", on each end. There are about 35 copies of Ty1 and at least 100 copies of delta (not always associated with Ty1) in the haploid genome. A few Ty1 elements are tandem and/or circular, but most are disperse and show (along with delta) some sequence divergence between repeat units. Sequence alterations involving Ty1 elements have been found during the continual propagation of a single yeast clone over the course of a month. One region with a large number of delta sequences (SUP4) also shows a high frequency of sequence alterations when different strains are compared. One of the differences between two such strains involves the presence or absence of a Ty1 element. The novel joint is at one inverted pair of delta sequences.
385 citations
TL;DR: There seemed to be a trend for reduction in C-heterochromatin content in the course of evolution in Cicer, and C-banding patterns allowed for chromosome identification and matching pairs of homologues in all species analyzed.
Abstract: Somatic karyotypes of the nine annual species of Cicer (2n = 16) were analyzed using C-banding. Highly significant differences in haploid genome length and C-band positive heterochromatin content were observed. The haploid genome length ranged from 20.0 μm in the wild species C. judaicum to 28.7 μm in the cultivated species C. arietinum, and significant differences for this character were observed between accessions within several species. Based on their heterochromatin content, the species were divided into two groups: low heterochromatin content (average of 41.7%), which included C. arietinum, C. chorassanicum, C. echinospermum, C. judaicum, C. pinnatifidum, C. reticulatum, and C. yamashitae, and high heterochromatin content (average of 59.5%), which included C. bijugum and C. cuneatum. Within-group variation for heterochromatin content was insignificant, while differences between groups were highly significant. There seemed to be a trend for reduction in C-heterochromatin content in the course of evolution in Cicer. In all species studied, C-bands were located proximally around the centromere with occasional bands in intercalary and distal positions. C-banding patterns allowed for chromosome identification and matching pairs of homologues in all species analyzed.
39 citations
TL;DR: The significance of the 4C value (where C is the amount of DNA in the unreplicated haploid genome) in angiosperm plants is discussed and some rules governing the distribution of DNA amount among different plant taxa are postulated.
Abstract: The significance of the 4C value (where C is the amount of DNA in the unreplicated haploid genome) in angiosperm plants is discussed. The DNA amount is a stable feature used in biosystematics. Although this parameter varies even in closely related taxa, there is no correlation between the DNA amount and the structural and functional organization of plants. The role of DNA amount, including "excess" DNA, in plant evolution is considered. Some rules governing the distribution of DNA amount among different plant taxa are postulated, together with the possibility of using the data in systematics, phylogeny, and solutions of problems of genetic apparatus organization and evolution. The decrease in DNA value per genome during plant evolution and the high level of species formation in taxa with large DNA values have been shown. Plant taxa with a small DNA value per genome have a high percentage and higher degree of polyploidy. The nature of the differential staining of euchromatin and heterochromatin bands of prophase and metaphase chromosomes is also discussed. Data that could explain the mechanism of heterochromatin visualization under cold pretreatment of cells are reviewed. Phenomena involved in the arrangement of chromocenters in interphase nuclei and chromosomes in metaphase during consecutive cell generations are discussed.
27 citations
TL;DR: In this article, a detailed account of experimental parameters useful in chromosome identification and evaluation of karyotype asymmetry is furnished citing suitable examples, and special emphasis is given to the quantitative parameter of "chromosome dispersion index" that promises phylogenetic differentiation of closely related karyotypes.
Abstract: Karyotype characterizing the phenotypic aspects of the chromosome complement represents structural and functional organization of the nuclear genome. Its constancy ensures transfer of the same genetic material to the next generation, while variation enables ecological differentiation and adaptation. Superimposition of karyotype information onto a phylogenetic framework has immense utility in elucidating direction of evolutionary change and delineation of taxonomic hierarchy. This article attempts to provide an illustrated description of the chromosomal features that are useful in discerning differences and affinities between species and taxa. A detailed account of experimental parameters useful in chromosome identification and evaluation of karyotype asymmetry is furnished citing suitable examples. In addition to various karyotypic indices, special emphasis is given to the quantitative parameter of “chromosome dispersion index (DI)” that promises phylogenetic differentiation of closely related karyotypes, since most genera of herbaceous angiosperms display interspecific differences in chromosome size and symmetry, if not number. Karyo-evolutionary trends involve both change in chromosome number, morphology/karyotype symmetry, ploidy and total haploid length. The pattern of DNA addition/deletion across the chromosome complement has been found to be variable. Such change in DNA is either equally shared by all the chromosomes or is proportionately shared commensurate to chromosome size, leading to differential pace of change in karyotype asymmetry across the taxa. The large data accumulating on chromosome number over the years offer opportunities to utilize them as additional tools in taxonomy. The basic chromosome number (ancestral haploid number) in angiosperms has been suggested as n = 7, and an ancestral 1C of 1.73 pg, which is characteristic of the major groups with slight deviation in certain orders. The average ‘holoploid genome size’ i.e. 1C, for the Angiosperms is inferred to be 5870 Mb/6.0 pg. However, the 1C-value data available for ca.10800 species of Angiosperms reveal genome size diversity ranging from 61 Mb/0.0648 pg in the carnivorous plant Genlisea tuberosa (Lentibulariaceae) to 1,49,000 Mb/152.23 pg in Paris japonica (Melanthiaceae) suggesting over 2400 fold variation across the angiosperms; and 230 fold variation within the family (0.66 pg in Schoenocaulon texanum vs. P. japonica with highest C value). Metaphase chromosome size is estimated to range from the shortest ~ 0.3 µm in Genlisea aurea, and at family level from ~ 0.8 µm in Chamaelirium luteum to ~ 30 µm in Paris japonica. Chromosome number ranges from n = 2 to 320 across the angiosperms, at family level from n = 4 to 120 in the Brassicaceae, and at genus level from n = 2 to 45 in Brachyscome (Compositae).The evolution has mostly been at the diploid level. It is generally believed that the chromosome size of monocots is larger than dicots and the chromosome size of temperate plants is larger than tropical plants. For a broader sense and larger scale understanding, the evolutional conception of karyotype is principally based on the thoughts that: (i) symmetrical karyotype is more primitive than asymmetrical ones, (ii) longer chromosomes are primitive than shorter ones, (iii) median centromeres with chromosome arms of equal length are more primitive than chromosome arms of unequal length, (iv) low basic numbers had given rise to higher ones, and the taxa with variable chromosome number are considered young and still in evolutionary flux, (v) species with one NOR site per haploid genome are considered advanced than multiple NOR sites, (vi) ancient species had less heterochromatin (repetitive DNA), the primitive species accredited heterochromatin, followed by gradual shedding of excess heterochromatin with evolutionary specialization. However, discovery of ancient episodes of Whole Genome Duplication (WGD) events said to have happened as an escape to the 5th mass extinction at the end of Cretaceous as a survival strategy has opened newer possibilities. A new thinking is beginning to emerge that concomitant with the climate change happening at a fast pace in the Anthropocene, it is likely that if global climate undergoes major change in coming centuries then auto-polyploidization could be the important player leading to increase in chromosome number.
18 citations
TL;DR: Interphase nuclear organization was studied in six species of Cicer and all the species showed chromocentric nuclear organization in both meristematic and differentiated cells instead of reticulate organization, which can be considered as primitive of the six Cicer species.
Abstract: Interphase nuclear organization was studied in six species of Cicer and all the species showed chromocentric nuclear organization in both meristematic and differentiated cells instead of reticulate organization. The number of chromocentres and treatment duration with acid or alkali were found to be species specific character. Percentage heterochromatin values determined by two different techniques were somewhat high in meristematic cells than those in differentiated cells. On the basis of heterochromatin values both in meristematic and differentiated cells C. reticulaturn can be considered as primitive of the six Cicer species. Nuclear organization was found to be governed by small size of chromosomes and low DNA content, but the relationship between heterochromatin values and DNA content was not clear.
8 citations
References
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TL;DR: The DNA of higher organisms usually falls into two classes, one specific and the other comparatively nonspecific, and it seems plausible that most of the latter originated by the spreading of sequences which had little or no effect on the phenotype.
Abstract: The DNA of higher organisms usually falls into two classes, one specific and the other comparatively nonspecific. It seems plausible that most of the latter originates by the spreading of sequences which had little or no effect on the phenotype. We examine this idea from the point of view of the natural selection of preferred replicators within the genome.
1,927 citations
TL;DR: Natural selection operating within genomes will inevitably result in the appearance of DNAs with no phenotypic expression whose only ‘function’ is survival within genomes.
Abstract: Natural selection operating within genomes will inevitably result in the appearance of DNAs with no phenotypic expression whose only ‘function’ is survival within genomes. Prokaryotic transposable elements and eukaryotic middle-repetitive sequences can be seen as such DNAs, and thus no phenotypic or evolutionary function need be assigned to them.
1,694 citations
"Chromosome banding in evolutionary ..." refers background in this paper
...Dover and Doolittle (1980) emphasize that, in establishing these processes, evolution has inadvertently endowed the genome with built-in mechanisms for irregular and recurrent random sequence rearrangements and created an environment in which elements capable (to varying extents) of promoting their own amplification and dispersion will inevitably arise (Dover 1977; Doolittle and Sapienza 1980; Orgel and Crick 1980)....
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TL;DR: Qualitatively, then, unequal crossover provides a reasonable and uncontrived explanation for the prevalence of highly repeated sequences in DNA and for the patterns of periodicity they evince.
Abstract: It is often supposed that highly repetitious DNA's arise only as a result of unusual mechanisms or in response to selective pressure. My arguments and simulations suggest, by contrast, that a pattern of tandem repeats is the natural state of DNA whose sequence is not maintained by selection. The simulations show that periodicities can develop readily from nonreptitious DNA as a result of the random accumulation of random mutations and random homology-dependent unequal crossovers. The lengths of these periodicities, and the patterns of subrepeats within them, would fluctuate in evolution, with the probability of a given pattern being dependent on the unknown exact nature of the crossover mechanism. Qualitatively, then, unequal crossover provides a reasonable and uncontrived explanation for the prevalence of highly repeated sequences in DNA and for the patterns of periodicity they evince.
1,143 citations
TL;DR: In this paper, Dispersed repetitive DNA sequences from yeast (Saccharomyces cerevisiae) nuclear DNA have been isolated as molecular hybrids in lambdagt and showed marked alterations in the size of the restriction fragments containing these repetitive DNAs.
446 citations