Non-homologue pairing and spontaneous meiotic interchanges in Drosophila melanogaster females

Abstract

Spontaneous interchange between the X chromosomes and the C(2 L) autosomal compound in their centromeric regions was studied in y/ XY;C(2L);(2R) and In(1)dl-49+B M1 / XY;C(2L);C(2R) Drosophila melanogaster females. These females were mated with F(2 L)/ F(2 L); C(2 R) males. Interchange occurrence was recorded as the appearance of an F 1 individual with a half-translocation of either X · 2 L or Y · 2 L type. 37 interchanges were recovered in y/ XY and 67 in In(1)/ XY females. The majority of the interchanges were of meiotic origin. The interchanges were mainly C(2L)- XY ; the most frequent type of half-translocation was Y · 2 L; dl-49+ B M1. Inversion increased about 5-fold the interchange frequency. In the course of C(2L)- XY interchange, the other X chromosome and C(2 R) compound regularly paired and disjoined. In y/ XY females, 8 crossover half-translocations of meiotic origin were recovered. The results obtained indicate that meiotic pairing between the X's and C(2 L) occurred in the females examined. According to our estimates, XY-C(2L) pairing is associated with interchange in the heterochromatic centrometric regions with a frequency of 10 −3. The recovery crossover half-translocations supports the chromocentral model of non-homologous pairing and allows us to assume that a chromosome may simultaneously pair with a homologue and a non-homologue. The disjunction pattern of this trivalent depends on its structure in each particular case. The chromosome-segregation pattern resulting from spontaneous interchanges was similar to that resulting from radiation-induced interchanges in the immature oocytes described by Parker. This similarity suggests that non-homologue pairing occurs in the immature oocytes too. The non-homologue-pairing pattern established by the interchange test conformed well with that previously established in y/ XY and In(1) XY females by the distribution test.