Abstract
IT is axiomatic that the chromosome complements of the different individuals comprising a species are identical in number and morphology. The North American ladybird beetle, C. stigma Say (= bivulnerus Muls.), constitutes one of the more striking exceptions in that different males may possess any number of chromosomes from 25 down to 19 (females, 26–20): it is a chromosomally polymorphic species1. The polymorphism here finds its basis in the centric fusion of non-homologous chromosomes, whereby an ‘A’ and a ‘B’ chromosome may be supplanted by an ‘A + B’ fusion chromosome. At meiosis two rod-shaped pairs may thus be replaced by one ring-shaped pair or, in the heterozygote, by a V-shaped configuration of three chromosomes.
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References
Smith, S. G., Experientia, 12, 52 (1956).
Smith, S. G., Proc. Tenth Intern. Cong. Genet., Montreal, 1, 444 (1959).
Smith, S. G., Ann. Rev. Entomol., 5, 69 (1960).
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SMITH, S. Tempero-Spatial Sequentiality of Chromosomal Polymorphism in Chilocorus stigma Say (Coleoptera : Coccinellidae). Nature 193, 1210–1211 (1962). https://doi.org/10.1038/1931210a0
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DOI: https://doi.org/10.1038/1931210a0
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