THE ROLE OF HETEROCHROMATIN IN MEIOTIC PAIRING OF MALE CHROMOSOMES IN DROSOPHILA-MELANOGASTER

The gamete spectrum of males containing metacentric chromosome 2 and combinations of 2R and 2L acrocentrics with heterochromatic regions of different size was studied. Changes in the size of the heterochromatic block located to the right of the centromere in the acrocentric 2L can alter the disjunction of this acrocentric, as well as that of the acrocentric of the opposite 2R arm. It is therefore concluded that, in addition to the major pairing site located at the base of arm 2L, the sites located in heterochromatin of the 2R arm also function during meiotic pairing in males. An account is given of the participation of a 2L acrocentric, containing Y-material at the telomeric end, either in pairing with metacentric chromosome 2 or with the X-chromosome, but not with both of them simultaneously. This phenomenon may be due to the spatial relations of pairing sites and the coiling of pairing chromosomes.