Nine morphologically distinct euchromatic B-chromosomes have been identified in Allium schoenoprasum from the River Wye, South Wales. The most common type (89%) is telocentric (Bt−1) and it is likely that the non-standard Bs are derivatives of Bt−1 by deletion, centric shift and/or centric misdivision. New B-types have also been produced from standard Bs in controlled crosses. In general, the Bs are mitotically extremely stable, although occasional plants, particularly those carrying non-standard Bs, are conspicuously variable in their B-constitution between root-tip cells. In addition, B-chromosome number is enhanced in some anthers of about one third of plants. Behaviour of B-chromosomes during meiosis is described. Although there is little bivalent formation, less than 5% of the Bs are lost during meiosis in anthers. There is, however, no evidence of B-chromosome accumulation in the offspring of controlled crosses, usually a slight loss, and Bs have deleterious effects on aspects of vigour and fertility. Thus, no satisfactory explanation for populations with up to 65% B-containing individuals has yet been found.
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Bougourd, S.M., Parker, J.S. The B-chromosome system of Allium schoenoprasum . Chromosoma 75, 369–383 (1979). https://doi.org/10.1007/BF00293478
- Developmental Biology
- Deleterious Effect
- Common Type
- Satisfactory Explanation
- Slight Loss