Nonhomologous pairing in oogonia and ganglia of Drosophila melanogaster

A high frequency of chromosome pairing between an X-duplication (Dp) and a compound 4 (-44), each of which lacks its homologue in the genome, has been observed in somatic ganglia cells in female and male larvae as well as in oogonia of adult Drosophila melanogaster. Three Dp's of different sizes were used. Pairing was determined both by inspection and by precise measurement of the distances between chromosomes; the two methods agreed in virtually every case. Nonhomologous pairing frequencies ranged from 23.0 to 62.6%, showing a strong dependency on size. The Dp that was closest in size to -44 produced the greatest frequency of pairing in each of the three tissues. Homologues in the same cells paired with a frequency of 89% or greater. The X and Y in the male ganglia showed a pairing frequency of only 45.7%, thus resembling nonhomologues in their pairing behavior. Genetic studies were also carried out on the three genotypes. Segregation data for the Dp's and -44 established that the same pattern of pairing observed in the mitotic cells was present in the oocytes - the Dp which was closest in size to the -44 again producing the greatest frequency of pairing. In the oocytes the pairing frequencies were much higher than those observed in the mitotic cells.