B chromosomes are extra chromosomes to the standard complement that occur in many organisms They can originate in a number of ways including derivation from autosomes and sex chromosomes in intraa

/pdf/b-chromosome-evolution-25cmhcd0kp.pdf

B-chromosome evolution.

The chapter focuses on the understanding of the mechanisms of sperm competition, which are essential for interpreting nonrandom patterns of paternity and for predicting the types of adaptations that sperm competition can generate. P2 values are often used to infer the mechanism of underlying patterns of sperm utilization: intermediate values are taken as indicative of sperm mixing while higher values of P2 are taken as evidence for sperm precedence or sperm displacement. The bimodal distribution of P2 values seen in Lepidoptera is an excellent example of how little the mean value of P2 can tell us about the patterns of sperm competition. Patterns of sperm competition can change markedly with changes in the intervals between copulations. It is clear that males can adjust the numbers of sperm ejaculated into females, depending on female quality and/or the risks of sperm competition. Thus, patterns of sperm utilization depend on the behavior of males. Alternatively, they also depend on the responses of females to males that vary in their quality as mates. Variation in the numbers of sperm inseminated into the female prior to the final mating can have marked effects on the patterns of sperm utilization.

10 – Sperm Competition in Insects: Mechanisms and the Potential for Selection

[A & B chromosomes. I].

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Bewildering Bs: an impression of the 1st B-Chromosome Conference

Satellite DNA (satDNA) is a major component yet the great unknown of eukaryote genomes and clearly underrepresented in genome sequencing projects. Here we show the high-throughput analysis of satellite DNA content in the migratory locust by means of the bioinformatic analysis of Illumina reads with the RepeatExplorer and RepeatMasker programs. This unveiled 62 satDNA families and we propose the term “satellitome” for the whole collection of different satDNA families in a genome. The finding that satDNAs were present in many contigs of the migratory locust draft genome indicates that they show many genomic locations invisible by fluorescent in situ hybridization (FISH). The cytological pattern of five satellites showing common descent (belonging to the SF3 superfamily) suggests that non-clustered satDNAs can become into clustered through local amplification at any of the many genomic loci resulting from previous dissemination of short satDNA arrays. The fact that all kinds of satDNA (micro- mini- and satellites) can show the non-clustered and clustered states suggests that all these elements are mostly similar, except for repeat length. Finally, the presence of VNTRs in bacteria, showing similar properties to non-clustered satDNAs in eukaryotes, suggests that this kind of tandem repeats show common properties in all living beings.

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High-throughput analysis of the satellitome illuminates satellite DNA evolution

A G banding technique combining trypsin and hot saline treatments was used to analyze the chromosomes of two grasshopper species, Eyprepocnemis plorans and Locusta migratoria, both of which contain both standard and supernumerary heterochromatin. Although this technique does not produce G bands like those in mammalian chromosomes, it serves to characterize heterochromatic regions whose nature has been inferred from other banding techniques (C, N, CMA, and DAPI banding). The light regions revealed by G banding contain GC-rich DNA sequences, the more prominent of which coincide with nucleolus organizer regions (NORs). Furthermore, the proximal heterochromatin in E. plorans was heterogeneous, and the standard and supernumerary heterochromatin showed conspicuous differences in organization. Supernumerary heterochromatin is an exception to the regular patterns shown by the standard heterochromatin. The findings are related to the mechanism of action of these banding techniques.Key words: banding techniques, gr...

/pdf/g-banding-in-two-species-of-grasshopper-and-its-relationship-17y2srf8rl.pdf

G banding in two species of grasshopper and its relationship to C, N, and fluorescence banding techniques

C-Heterochromatin content of supernumerary chromosome segments of grasshoppers: Detection of an euchromatic extra segment

C-heterochromatin content of supernumerary chromosome segments of grasshoppers: detection of an euchromatic extra segment

Twenty-eight progeny analyses (PAs) performed on specimens of E. plorans collected from four natural Iberian populations have been informative about the transmission of rare B chromosome types or the de novo origin of some of them. At least 11 rare B-types have been found in addition to the predominant ones: B1 in Daimuz, B2 in Jete and Salobrena, and B5 in Fuengirola. The presence in two controlled crosses of one embryo carrying a B-type which was absent in the parents suggests that these B variants (B2iso and B1f1) have originated de novo. Eleven other PAs suggest that new B derivatives are recurrently arising in these populations. The most frequent B chromosome mutation was centromere misdivision that originated four different B-types (B2m1, B1iso, B2iso and Bmini). Other rearrangements were pericentric inversions (B2i1, B2i2 and B2i3), inverse tandem fusion (B2it1), centric fusion (B1f1) and deletions (B2d1 and B2d2). The four B derivatives produced by centromeric misdivision are significantly eliminated during sexual transmission, most probably owing to deficiencies in the control of chromosome movement by their hemicentromeres. Those derived from translocations showed Mendelian transmission but deletion B variants showed a tendency to elimination. Our results suggest that B chromosome substitution of B1 by B2 in the Salobrena and Jete populations could be achieved by differences in relative transmission efficiency, as in one controlled cross, where the female carried 1 B1 plus 1 B2, B2 was significantly overtransmitted and B1, eliminated.

/pdf/generating-high-variability-of-b-chromosomes-in-8113sirgmx.pdf

Generating high variability of B chromosomes in Eyprepocnemis plorans (grasshopper)

Mitotic instability of B chromosomes has been studied in males and females from two Spanish populations of Locusta migratoria. This instability is a common feature in embryos, adult somatic tissues such as gastric caeca, and ovariole wall cells and male and female germ lines. While B chromosomes accumulate in the male germ line independently of the existence or absence of intraindividual variation in the number of B chromosomes in gastric caeca cells, they do not accumulate in the female germ line despite meiotic instability. The relationship between the mitotic instability of the B chromosomes in germ lines and their mode of transmission is discussed.Key words: Locusta migratoria, B chromosomes, mitotic instability, accumulation.

Relationship between mitotic instability and accumulation of B chromosomes in males and females of Locusta migratoria.

Three types of double crosses were carried out to investigate sperm competition in the grasshopper Eyprepocnemis plorans. Maximum likelihood estimation of paternity probability showed a high degree of second male sperm precedence (P2 = 90%). The results also showed that: (i) a single copulation may be enough for an efficient paternity displacement; (ii) males do not use sperm plugs, but they mate for a prolonged period of time to resist further copulation; and (iii) successive paternity displacements may be seen in the same female. The mechanisms controlling sperm competition in E. plorans, and the evolutionary implications of this phenomenon are discussed

/pdf/paternity-displacement-in-the-grasshopper-eyprepocnemis-18ny82dlxw.pdf

E Viseras

Papers

G banding in two species of grasshopper and its relationship to C, N, and fluorescence banding techniques

C-heterochromatin content of supernumerary chromosome segments of grasshoppers: detection of an euchromatic extra segment

Generating high variability of B chromosomes in Eyprepocnemis plorans (grasshopper)

Relationship between mitotic instability and accumulation of B chromosomes in males and females of Locusta migratoria.

Paternity displacement in the grasshopper Eyprepocnemis plorans