Polyploids — organisms that have multiple sets of chromosomes — are common in certain plant and animal taxa, and can be surprisingly stable. The evidence that has emerged from genome analyses also indicates that many other eukaryotic genomes have a polyploid ancestry, suggesting that both humans and most other eukaryotes have either benefited from or endured polyploidy. Studies of polyploids soon after their formation have revealed genetic and epigenetic interactions between redundant genes. These interactions can be related to the phenotypes and evolutionary fates of polyploids. Here, I consider the advantages and challenges of polyploidy, and its evolutionary potential.

/pdf/the-advantages-and-disadvantages-of-being-polyploid-3szbdyr9u1.pdf

The advantages and disadvantages of being polyploid

Nuclear DNA Amounts in Angiosperms

The number of angiosperm species for which nuclear DNA amount estimates have been made has nearly trebled since the last collected lists of such values were published, and therefore, publication of a more comprehensive list is overdue. This paper lists absolute nuclear DNA amounts for 753 angiosperm species. The data were assembled primarily for reference purposes, and so the species are listed in alphabetical order, as this was felt to be more helpful to cyto- and biochemists whom, it is anticipated, will be among its major users. The paper also reviews aspects of the history, nomenclature, methods, accuracy and problems of nuclear DNA estimation in angiosperms. No attempt is made to reconsider those aspects of nuclear DNA estimation which have been fully revised previously, although the bibliography of such aspects is given. Instead, the paper is intended as a source of basic information regarding the terminology, practice and limitations of nuclear DNA estimation, especially by Feulgen microdensitometry, as currently practiced.

▪ Abstract Here we review the biology of early generation neopolyploids and discuss the profound changes that accompany their formation. Newly formed auto- and allopolyploids exhibit considerable meiotic complexity, including multivalent pairing, multisomic inheritance, and the production of unbalanced gametes. The cytogenetic behavior of allopolyploids and autopolyploids differ statistically, but are more similar than commonly believed. The progeny of neopolyploids include a high frequency of aneuploids, pseudoeuploids and homeologue-recombinant genotypes that may contribute to the phenotypic variability observed in early generation polyploids. We find no evidence to support the traditional view that autopolyploids possess lower fertility than allopolyploids, casting doubt on the paradigm that allopolyploids should be more frequent due to their inherent fertility. The fertility of early generation polyploids increases rapidly, owing largely to selection against meiotic configurations that generate unbala...

/pdf/neopolyploidy-in-flowering-plants-o3qdtfazt6.pdf

Neopolyploidy in flowering plants

The role of polyploidy per se in the development of evolutionary novelty remains one of the outstanding questions in flowering plant evolution. Since chromosome doubling usually is associated with hybridization, the effects of doubling are difficult to uncouple from those of hybridity and recombination. Synthetic polyploids in crops typically are inferior to their diploid counterparts under conditions to which the diploids are adapted. This observation has suggested to many that chromosome doubling is a hindrance to progressive evolution. Evidence is presented herein from biochemical, physiological, developmental, and genetical sources which indicates that the nucleotypic effects of chromosome doubling are not necessarily negative. Indeed chromosome doubling may "propel" a population in to a new adaptive sphere, and render it capable of occupying habitats beyond the limits of its diploid progenitor. This postulate is consistent with what we know of the ecological tolerances of diploids and related polyplo...

Polyploidy and Novelty in Flowering Plants

Genotypic control of chromosome behaviour in rye X. Chromosome pairing and fertility in autotetraploids

/pdf/genotypic-control-of-chromosome-behaviour-in-rye-x-izsko24a93.pdf

2C nuclear DNA amounts in diploid species of the genus Vicia (x = 5, 6, and 7) range from approximately four to twenty seven picograms. The DNA amount varies independently of the chromosome number and of taxonomic grouping within the genus. Comparisons of the distribution of DNA amounts among chromosomes within the complements show that increase in total nuclear DNA amount within the genus is achieved by equal increments to each chromosome independent of size i.e., small chromosomes acquire the same amount of extra DNA as the large chromosomes. An inevitable consequence of such a pattern of DNA change is that the chromosomes within complements with high DNA amount are more alike in size and DNA content, more symmetrical, than within complements of species with low DNA amount. In a few species the symmetry is confounded as a result of Robertsonian fusion. The equal distribution of extra DNA among chromosomes within a complement has been reported in other genera of flowering plants viz. in Lolium, Festuca and Lathyrus. In all cases there is evidently a severe constraint either upon the way in which the nuclear DNA variation is achieved or else upon its persistence in the face of selection. Since the pattern of change affects the relative sizes of chromosomes within complements we conclude that relative size may itself be of adaptive importance.

/pdf/dna-variation-between-and-within-chromosome-complements-of-379lqf2mgr.pdf

DNA variation between and within chromosome complements of vicia species

In the genus Lathyrus the divergence and evolution of species was accompanied by large scale changes in nuclear DNA amount. All the species are diploids with 14 chromosomes so that the DNA changes were the result of amplification or deletion of segments within chromosomes. Our evidence indicates that the quantitative changes involve mainly the repetitive, as distinct from the non-repetitive fraction of the chromosomal DNA and, on a cytological basis, mainly heterochromatin in contrast to euchromatin. There is an element of discontinuity in the distribution of DNA amounts among species which suggests that the DNA variation results from a series of separate, spasmodic events. The discontinuities may be viewed, also, as “steady states” from the standpoint of genetic balance and biological fitness.

Nuclear DNA variation in Lathyrus

/pdf/chromosome-evolution-in-lolium-4i9i5b6c4i.pdf

Chromosome evolution in Lolium

DNA amounts, by microdensitometry, are underestimated in nuclei with high DNA density A method is described for correcting the DNA readings in DNA dense nuclei DNA measurements in the allotetraploid Brassica napus (2n = 38), B carinata (2n = 34) and B juncea (2n = 36), after applying the correction, were found to equal the sum of the diploid parents from which they are derived This finding, contrary to previous reports, refutes the evidence for a nuclear DNA diminution subsequent to the formation of the allotetraploids Interphase nuclei in newly synthesised allotetraploids are substantially larger than in long established allotetraploids It is suggested that the reduction in nuclear size in tetraploids is associated with greater condensation of chromosome material which, in turn, may reflect an adaptive “switching off” of redundant gene copies in the tetraploid complement

/pdf/nuclear-dna-and-the-evolution-of-allotetraploid-brassicae-4k54m2j4fb.pdf

Nuclear DNA and the evolution of allotetraploid Brassicae

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