Abstract
In a sample of 85 males of the grasshopper Melanoplus femur-rubrum, three different supernumerary chromosomes (B-chromosomes) were observed: a medium-sized metacentric, BM, present in 12.9% of the males and two small telocentrics, BT and Bt, present in 8.2% and 3.5% of the males, respectively. The BM element is mitotically stable, while the BT and Bt elements are mitotically unstable, exhibiting numerical variation among testicular follicles. The mean number of B's per male (testis) is 1.00, 1.62, and 1.38 for the BM, BT, and Bt elements, respectively. A study of chiasma frequency among A-chromosomes revealed that there are no significant differences among the zero B and various B classes either for chiasma frequency or for the variation in chiasma frequency between individuals. There was, however, evidence for a higher within-individual variation in B-containing males when these were pooled. Cells with two Bt-chromosomes were regularly missing the smallest pair of A-chromosomes, suggesting that the Bt element induces non-disjunction of a pair of A-chromosomes and, possibly, that the Bt-chromosome is derived from the missing A-chromosome.
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Portions of this study were submitted by R. T. Stephens in partial fulfillment of the requirements for the degree of Master of Arts, Department of Biology, State University College, New Paltz, New York.
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Stephens, R.T., Bregman, A.A. The B-chromosome system of the grasshopper Melanoplus femur-rubrum . Chromosoma 38, 297–311 (1972). https://doi.org/10.1007/BF00290927
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DOI: https://doi.org/10.1007/BF00290927