Meiotic disjunction and embryonic lethality in trisomies derived from an X-linked translocation in the onion fly,Hylemya antiqua (Meigen)

Translocation- and tertiary trisomies (for the X-chromosomes) were obtained after testcrossing translocation heterozygous females of an X-linked “simple” translocation stock. Meiotic disjunction as judged from segregations at M II (males) and in young eggs of testcrosses (males and females) in translocation trisomics was studied. No progeny of tertiary trisomic males and females was found, but male M II could be studied. Six different orientation types appeared in translocation trisomie (2n + 1) males and these were present in equal frequencies. No adjacent II configurations were found. The small X- and Y-chromosomes and the large translocated X-chromosome of the translocation complex disjoin at random (n and n + 1 gametes) in both translocation- and tertiary trisomic males. In translocation trisomic females four different orientation types appeared. From the high frequency of two of these (together, 94.5%) it is concluded that the two normal X-chromosomes show preferential pairing and disjunction, while the translocated X-chromosome moves to either one of the two poles at random. Primary trisomic (for the X-chromosome) males (XXY) and females (XXX) were obtained from testerossed translocation trisomics. Cytological analysis of adult male progeny of testerossed XXY males showed that no random orientation for the X-, X- and Y-chromosomes occurred because half of the sons was disomic (XY) and half of them trisomic (XXY). A possible mechanism is discussed. Analysis of young eggs of testerossed XXX females indicated a segregation of 2X∶1X=1∶1. The level of “semi”-sterility as scored from testcrosses of translocation trisomies appeared to be as in translocation heterozygotes. Here again a close relation exists between “semi”-sterility and deficiencies in eggs for a large chromosomal segment. The possible use of this translocation for genetic control of insect pests is discussed.