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B chromosomes in Brazilian rodents
M J J Silva1, Y Yonenaga-Yassuda
1Departamento de Biologia, Instituto de Biociências, Universidade de São Paulo-Rua do Matão, São Paulo, SP, Brazil. mariajo@usp.br
Cytogenetic and Genome Research
|August 5, 2004
Summary
Accessory B chromosomes are identified in eight Brazilian rodent species. These B chromosomes exhibit variations in structure and behavior during meiosis, with active NORs found in two species.
Area of Science:
- Genetics
- Cytogenetics
- Mammalian Biology
Background:
- B chromosomes, or supernumerary chromosomes, are found in various organisms and can influence phenotypic traits.
- Their presence and characteristics can vary significantly between species and populations.
- Understanding B chromosome behavior is crucial for evolutionary and genetic studies.
Purpose of the Study:
- To document the occurrence of B chromosomes in Brazilian rodent species.
- To characterize the structural and meiotic properties of these B chromosomes.
- To investigate the presence of active nucleolar organizing regions (NORs) on B chromosomes.
Main Methods:
- Karyotypic analysis of eight Brazilian rodent species.
- Fluorescence in situ hybridization (FISH) to detect interstitial telomeric signals.
- Analysis of meiotic behavior, including synaptonemal complex formation.
- Detection of active NORs using specific staining techniques.
Main Results:
- B chromosomes were identified in eight Brazilian rodent species.
- These B chromosomes showed heterogeneity in size, morphology, banding patterns, and NOR/telomeric signal presence.
- Most B chromosomes were heterochromatic and late replicating.
- Active NORs were observed on B chromosomes in Akodon montensis and Oryzomys angouya.
- B chromosomes typically behaved as univalents or bivalents during meiosis, without pairing with autosomes or sex chromosomes.
Conclusions:
- Brazilian rodents exhibit diverse B chromosome systems.
- B chromosome characteristics, including NOR activity, vary among these species.
- The meiotic behavior suggests B chromosomes are largely independent of the standard chromosome set.
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