Journal Article

A Century of B Chromosomes in Plants: So What?

R. Neil Jones, Wanda Viegas and Andreas Houben

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 6, pages 767-775
Published in print April 2008 | ISSN: 0305-7364
Published online August 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm167
A Century of B Chromosomes in Plants: So What?

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background

Supernumerary B chromosomes (Bs) are a major source of intraspecific variation in nuclear DNA amounts in numerous species of plants. They favour large genomes, and create polymorphisms for DNA variation in natural populations. By studying Bs we can gain useful knowledge about the organization, function and evolution of genomes. There are also significant biological questions concerning the origin and structural organization of Bs, and the way in which these selfish elements can establish themselves by exploiting the replicative machinery of their host genome nucleus.

Scope

It is a sine qua non that Bs originate from the A chromosomes, in a variety of ways. We can study their modes of drive and ask how it is that chromosomes which apparently lack genes can have control over their own drive process which leads to their survival in natural populations. Molecular cytogenetic studies are opening up new avenues of investigation. Population equilibria for B frequencies are determined by a balance between accumulation and harmful effects. Bs are also subject to meiotic loss due to polysomy and to elimination at meiosis as univalents. These balancing forces can be seen in the context of host/parasite interaction, based on a dissection of the genetic elements in both As and Bs (in maize) which interact to bring about a stable equilibrium, at least for a snapshot in time.

Conclusions

Aside from their intrinsic enigmatic properties, B chromosomes make useful experimental tools to study genome organization. Thus far they have not been exploited for their applications, other than through the use of A-B translocations used for gene mapping in maize; but there are opportunities to use them to modulate the frequency and distribution of recombination, to diploidize allopolyploids, to study centromeres and to be developed as plant artificial chromosomes; given that they can be structurally modified and their inheritance stabilized.

Keywords: B chromosomes; DNA polymorphisms; host/parasite interaction; mitotic/meiotic drive; applications; genome organization/evolution; centromeres

Journal Article.  6506 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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