1)

Almost all polyploids arise by way of unreduced gametes; other mechanisms occur, but are negligible.




2)

The most widespread and common event is (2n+n) reproduction.




3)

Triploids so produced frequently yield 4X plants on backcrossing and 6X plants on selfing.




4)

Spontaneous polyploids appear repeatedly, but their fate depends on vigor and competitive ability.




5)

The polyploids most frequently produced are probably strict autoploids, but they often lack competitive ability and may not become successfully established.




6)

Wide crosses occur in nature but not very often; if the hybrid is vigorous, it may yield a stable, fertile polyploid in the second or later generations via unreduced gametes.




7)

Wide crosses by way of (2n+n) reproduction are probably more common and successful than the above (6) pathway.




8)

The most likely pathway to a successful polyploid in nature involves neither wide crosses nor strict autoploidy but crosses between races, ecotypes and cytotypes within a biological species.




9)

The more or less autoploids so produced may generate genuine alloploids by interspecific hybridization at polyploid levels.




10)

The classic explanation of alloploidyvia “chromosome doubling” of a sterile diploid interspecific hybrid is misleading in most cases, and this route is probably negligible in the evolution of polyploid systems.

https://link.springer.com/content/pdf/10.1007/BF02860830.pdf

On Ö. Winge and a Prayer: The origins of polyploidy

OTHER WHEAT GENES AFFECTING PAIRING . . ....... . . . . . . . . ......... . . . . ........ ...... 37 Promoters of Pairing 37 Suppressors of Pairing 38 GENES IN OTHER SPECIES THAT AFFECT PAIRING 39 THE EFFECT OF ACCESSORY CHROMOSOMES , 40

Genetic Control of Chromosome Pairing in Wheat

An apparent deletion of Ph, the chromosome-5B suppressor of homoeologous pairing, was obtained by X-raying normal pollen and using it on plants monosomic for a 5B chromosome carrying the marker Hai...

Genetics society of canada award of excellence lecture an induced mutant with homoeologous pairing in common wheat

A Glossary of Genetics and Cytogenetics

Publisher Summary The sole important development in fern cytological technique has been the development of a variety of squash methods for the study of fern chromosomes in somatic tissues. This chapter reviews the evolutionary patterns and processes in ferns. The fossil record of the polypodiaceous ferns in Mesozoic era and tertiary period are also reviewed. The Thelypteridaceae is a large and axonomically difficult family, whose classification is in an only partially resolved state, whereas, the Dryopteridaceae is a large and morphologically diverse but cytologically remarkably uniform family. The existence of a great natural group of genera, the Adiantaceae is also presented in the chapter. The cytology of some of the ancient ferns such as Psilotales, Ophioglossales, Marattiales, and Osmundales are discussed. The information necessary for evaluation of the contribution that cytology can make towards a true phylogenetic classification of the ferns is presented here showing the basic chromosome number or numbers determined for each genus. The different types of polyploidy found in ferns namely autopolyploidy, allopolyploidy, segmental alloploidy and autoallopolyploidy, and their occurrence in different species complexes are also discussed. The systematic and geographical distribution of polyploids, irrespective of their genetic nature, is also reviewed.

Evolutionary Patterns and Processes in Ferns

Publisher Summary This chapter discusses the genetic variation in chromosome pairing Alterations in the behavior of chromosomes at meiosis are known to result from genetic variation as well as from differences in several environmental factors The operation of selection on genetically controlled variation in the chromosomal phenotype is responsible for the development of meiotic mechanisms adapted to the requirements of the breeding structures of species and of their populations The fertility of an organism and consequently the fitness of the lineage to which it belongs are intimately related in sexual forms and in some apomicts, to the efficiency of the over-all meiotic process The prime function, upon which the efficacy of the process depends, is the segregation of homologous chromosomes Two distinct aspects of the process of meiotic chromosome pairing are therefore under genetic control The extent to which synapsis is realized within the chromosome complement is determined by the activities of major genes and polygenes and by interactions within the genetic system comprised of relevant genes of both kinds The specificity of synapsis is widened or narrowed by gene action to permit the pairing of chromosomes distantly or closely related genetically and evolutionarily

Genetic Variation in Chromosome Pairing

Recombination results in the release of variation upon which selection is practised in plant breeding. However, according to the objectives of the programme it may be necessary to reduce recombination to limit the disturbance of arrangements of genes already well suited to agricultural needs or to increase recombination to maximize the likelihood of recombination's giving rise to transgressive segregation. Appropriate breeding manipulations are discussed. In addition, descriptions are provided of the induction of recombination between chromosomes that are distantly related in evolution and between which meiotic pairing and recombination does not normally take place.

C. N. Law

Papers

Genetic Variation in Chromosome Pairing

The Control of Recombination