B Chromosomes

Camacho, Juan Pedro M.

doi:10.1016/b978-012301463-4/50006-1

Cited by 198 publications

(182 citation statements)

References 229 publications

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“…In addition, B chromosomes typically do not recombine with A chromosomes and they are prone to gene mutational inactivation (McVean 1995). Therefore, the life cycle of a B chromosome can pass through a number of successive parasitic/driving and neutralized/nondriving stages (Camacho 2005), implying that the evolutionary status of a B chromosome may not be useful to estimate the age and origin of a B chromosome.…”

mentioning

confidence: 99%

“…Battaglia (1964) first proposed that B chromosomes could arise during interspecies mating (e.g., McAllister and Werren 1997;Perfectti and Werren 2001). But B chromosomes could also arise as a by-product of A chromosome evolution (see Camacho 2005). This intraspecific origin implies that B chromo-1 somes should be made up of the same kind of DNA sequences present in the A chromosomes, making it unlikely to find DNA sequences exclusive to B chromosomes.…”

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confidence: 99%

“…Although B chromosomes are usually enriched in satellite DNA, these sequences are also abundant in the A genome, particularly in heterochromatin. These repetitive elements contribute to the heterochromatic nature of B chromosomes (Camacho 2005). Since heterochromatinization is a known mechanism of gene silencing and inactivation (Weiler and Wakimoto 1995), the highly heterochromatic nature of these chromosomes could explain why only a few B chromosomes are known to affect phenotypes (Camacho 2005).…”

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confidence: 99%

“…These chromosomes are considered genome parasites because they usually diminish host fitness (Ö stergren 1945;Jones 1985). In spite of their deleterious effects, they manage to maintain themselves in natural populations because they frequently show higher transmission rates (i.e., drive) than A chromosomes (for review, see Camacho 2004Camacho , 2005Jones et al 2008). The existence of a drive mechanism in the germ line ensures B chromosome invasiveness in natural populations.…”

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confidence: 99%

“…B chromosomes (also known as supernumerary or accessory) are dispensable chromosomes found in some individuals of .2000 eukaryotic species (Camacho 2005). These chromosomes are considered genome parasites because they usually diminish host fitness (Ö stergren 1945;Jones 1985).…”

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confidence: 99%

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A Single, Recent Origin of the Accessory B Chromosome of the Grasshopper Eyprepocnemis plorans

Muñoz-Pajares

Martínez-Rodríguez²,

Teruel³

et al. 2011

Genetics

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B chromosomes are dispensable chromosomes found in .2000 eukaryotic species, usually behaving as genomic parasites. Most B chromosomes seem to be made up of the same kind of DNA sequences present in the A chromosomes. This sequence similarity makes it difficult to obtain specific molecular probes that may permit B-presence diagnosis without cytogenetic analysis. We have developed a sequencecharacterized amplified region (SCAR) marker for B chromosomes in the grasshopper Eyprepocnemis plorans, which specifically amplifies a 1510-bp DNA fragment exclusively in B-carrying individuals. Fluorescent in situ hybridization and fiber FISH analyses showed that this marker is a tandemly repeated DNA sequence closely intermingled with 45S rDNA. PCR reactions showed the presence of SCAR-like sequences in the A chromosomes, but in two separate fragments, supporting the intraspecific origin of B chromosomes in this species. SCAR marker DNA sequence showed to be identical in B chromosome variants from several localities from Spain and Morocco, and it was very similar to those found in B chromosome variants from Greece and Armenia. This strongly suggests that this sequence was already present in the ancestral B chromosome of this species. In addition, the scarce sequence variation observed among several B variants from very distant populations suggests either a functional constraint or, more likely, a recent and unique origin for B chromosomes in this species.

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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A Single, Recent Origin of the Accessory B Chromosome of the Grasshopper Eyprepocnemis plorans

Muñoz-Pajares

Martínez-Rodríguez²,

Teruel³

et al. 2011

Genetics

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Extensive variation in chromosome number and genome size in sexual and parthenogenetic species of the jumping‐bristletail genus Machilis (Archaeognatha)

Gassner

Dejaco

Schönswetter

et al. 2014

Ecology and Evolution

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Parthenogenesis in animals is often associated with polyploidy and restriction to extreme habitats or recently deglaciated areas. It has been hypothesized that benefits conferred by asexual reproduction and polyploidy are essential for colonizing these habitats. However, while evolutionary routes to parthenogenesis are manifold, study systems including polyploids are scarce in arthropods. The jumping-bristletail genus Machilis (Insecta: Archaeognatha) includes both sexual and parthenogenetic species, and recently, the occurrence of polyploidy has been postulated. Here, we applied flow cytometry, karyotyping, and mitochondrial DNA sequencing to three sexual and five putatively parthenogenetic Eastern-Alpine Machilis species to investigate whether (1) parthenogenesis originated once or multiply and (2) whether parthenogenesis is strictly associated with polyploidy. The mitochondrial phylogeny revealed that parthenogenesis evolved at least five times independently among Eastern-Alpine representatives of this genus. One parthenogenetic species was exclusively triploid, while a second consisted of both diploid and triploid populations. The three other parthenogenetic species and all sexual species were diploid. Our results thus indicate that polyploidy can co-occur with parthenogenesis, but that it was not mandatory for the emergence of parthenogenesis in Machilis. Overall, we found a weak negative correlation of monoploid genome size (Cx) and chromosome base number (x), and this connection is stronger among parthenogenetic species alone. Likewise, monoploid genome size decreased with elevation, and we therefore hypothesize that genome downsizing could have been crucial for the persistence of alpine Machilis species. Finally, we discuss the evolutionary consequences of intraspecific chromosomal rearrangements and the presence of B chromosomes. In doing so, we highlight the potential of Alpine Machilis species for research on chromosomal and genome-size alterations during speciation.

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Are B chromosomes useful for crop improvement?

Jones

Ruban

2019

Plants People Planet

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Societal Impact Statement Ensuring the sustainable production of food within the context of an increasing world population is a huge challenge facing humankind. Here we review the existence of additional, non‐essential chromosomes, known as B chromosomes, and consider their potential usefulness for crop improvement. These enigmatic chromosomes have long fascinated scientists and although their origin and function in plants is somewhat obscure, new research is beginning to shed light on these mysterious chromosomes. This work suggests that B chromosomes may be useful for crop improvement, particularly in grasses, where they show promise as a mechanism to introduce new genes, which could potentially help us to produce more efficient crops. Summary The question of the usefulness of supernumerary B chromosomes (Bs) has long fascinated cytogeneticists. Since their discovery in 1907 thousands of species with Bs have been discovered, but their function in the genetics system remains enigmatic, from their origin, evolution, and adaptive significance, as well as their molecular structure and organization. New research is beginning to answer some of these tantalizing questions. Here, we summarize the known data and conclude that Bs are potentially useful, but only in a few known cases, especially in the grasses, and notably in terms of their engineering as plant artificial chromosomes (mini‐chromosomes) to carry whole suites of transgenes outside of, and free from interference with, the normal genome.

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B Chromosomes

Cited by 198 publications

References 229 publications

A Single, Recent Origin of the Accessory B Chromosome of the Grasshopper Eyprepocnemis plorans

A Single, Recent Origin of the Accessory B Chromosome of the Grasshopper Eyprepocnemis plorans

Extensive variation in chromosome number and genome size in sexual and parthenogenetic species of the jumping‐bristletail genus Machilis (Archaeognatha)

Are B chromosomes useful for crop improvement?

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