ISSN:
1573-6857
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract An investigation of nondisjunction inDrosophila hydei has disclosed that spontaneous primary nondisjunction of the X chromosomes occurs with a frequency of 1/13000, and secondary nondisjunction with a frequency of 1/3500. These rates are much lower than the ones previously reported forDrosophila melanogaster which are about 1/1000 for primary nondisjunction and 1/50 for secondary nondisjunction. The low rate of secondary nondisjunction inhydei is attributed to the much greater genetic length of the X chromosome and the corresponding reduction in noncrossover X's available for distributive pairing with the Y chromosome. The low rate of primary nondisjunction is attributed to both a reduction in noncrossover X chromosomes, and to the large heterochromatic arm of the X chromosome which, it is suggested, makes the X centromere a strong centromere. Thus, it is further suggested, the reduction in noncrossover chromosomes reduces the opportunity for nonhomologous distributive pairing and nondisjunction of the type involving noncrossover chromosomes. Nondisjunction of the type involving crossover chromosomes then is prevented by the success of the strong centromeres in overcoming “entanglements” that would lead to nondisjunction in the case of ordinary or weak centromeres.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01557152
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