Meiotic segregation of five different reciprocal translocations in the onion fly, Hylemya antiqua (Meigen).

For one translocation (T14) with short interstitial segments in Hylemya antiqua significant differences in segregation behaviour between males and females were observed. In males the ratio of alternate:adjacent 1:adjacent 2 was approximately 7:3:0 and in females about 8:1:3. This difference is attributed to the difference in type of chromosome association. Female meiosis is chiasmate and male meiosis is achiasmate. It is suggested that meiotic pairing in males results in relative short "Coorientation Determining Distances" (CDDs) between homologous centromeres which favours alternate and adjacent 1 segregation. In females because of non-localized chiasmata on the average no differences in CDD between homologous and nonhomologous centromeres are expected. This might explain the occurrence of coorientation between non-homologous centromeres resulting in adjacent 2 segregations. Four other translocations with longer interstitial segments than T14 showed in males as well as females predominantly an alternate and adjacent 1 segregation, adjacent 2 was hardly found (0-3.6%). The longer distance between non-homologous centromeres is probably the reason.