| Abstrakt: |
Populations of Allium schoenoprasum, 2n=16, from six of the eight British localities have been examined. A B-chromosome polymorphism has been found which is limited to the River Wye, South Wales, where A. schoenoprasum grows along a 15 kilometre stretch. Four interrelated types of small, euchromatic, mitotically-stable B-chromosomes occur. Twelve different B-karyotypes, including an individual with 18 Bs, have been recorded. Populations contain up to 39% of plants with Bs. The B-chromosomes are not uniformly distributed along the river but are limited to populations in the downstream part of the range. An abrupt change from 34% to 0% B-contaiuing plants takes place over only 1.2 kilometres. The unique combination of riverside populations in linear order and the sudden discontinuity in the cytological structure of these populations may enable the factors influencing B-chromosome distribution to be established. |
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