Abstract
Populations of Crepis capillaris to the south of latitude 53° 30′N in Britain are often polymorphic for the presence of B-chromosomes. Individual plants may have 0B, 1B or rarely 2B. Eleven out of 24 southern populations carried B-chromosomes with an overall average of 14 per cent B-containing plants in polymorphic populations. The maximum frequency of B-containing plants observed in a population was 25 per cent. In a detailed survey of Bredon Hill, Hereford and Worcester, B-chromosomes reached maximum frequencies at mid-altitudes in large populations, declining both towards the summit and in the small, isolated lowland populations. It is suggested that Bs in Crepis are excluded from populations growing under sub-optimal conditions. B-frequency in a population at East Wretham Heath, Norfolk, remained constant over three generations despite a very strong accumulation mechanism operating in C. capillaris. Selection must operate against individuals with one or more B-chromosomes to maintain this constancy.
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Parker, J., Jones, G., Edgar, L. et al. The population cytogenetics of Crepis capillaris IV. The distribution of B-chromosomes in British populations. Heredity 66, 211–218 (1991). https://doi.org/10.1038/hdy.1991.27
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DOI: https://doi.org/10.1038/hdy.1991.27
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