The B chromosome system of Melanoplus Femur-rubrum
Flinn, Ronald R.
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Thirteen populations of the grasshopper species Melanoplus femur-rubrum were surveyed for B chromosome frequency distribution. Two populations were surveyed eight times during a single season and three times during a single day in an attempt to detect B frequency variations. Several populations were intensively analyzed for variations in B chromosome morphology and activity. Results of these analyses revealed that B frequency variations occur between isolated populations but remain stable for one population between yearly samples, during a single meiotic season and throughout a single day. Four possible types of B chromosomes were described. Both individual and populational differences in B chromosome activity during meiosis were recorded. Chromosome area studies revealed that the area of the X chromosome is significantly reduced at metaphase I when B chromosomes are present in the same cell. No variations in chiasma frequency were found in the populations analyzed. Chromosome arm length studies revealed that the origin of the three major B chromosome types is most likely one of the smallest three autosomes. Several other structural anomalies involving the X and autosomes are described.