Cytogenetics of inherited partial sterility in three generations of the large milkweed bug as related to holokinetic chromosomes

AdultOncopeltus fasciatus males were irradiated with 9000 R of X-rays, and crossed to untreated females. Fertility was reduced to 4.1%. F₁ males and F₂ and F₃ males and females were outcrossed to untreated partners. All F₁ males were partially or totally sterile and a significant number of F₂ and F₃ males and females had reduced fertility. The fertility of each generation was higher than the preceding one, even though the progeny studied in the 3rd generation were selected mostly from low-fertility lines. Cytogenetic studies showed that complex chromosome rearrangements and fragments were transmitted to each generation and were severe enough to account for reduced fertility. — The transmission of complex chromosome rearrangements and fragments for 3 generations of outcrossing correlates with the persistence of sterility in this species possessing holokinetic chromosomes. — Over half the inviable embryos derived from irradiated sperm from P₁ males died in the early stages of development. The inviable embryos produced in later generations died in much later stages of development. — A stable rearrangement of a Y-chromosome fragment translocated to an autosome was isolated from a single F₁ male. This rearrangement was transmitted to all F₂ and F₃ sons. Fertility of the males of this line was reduced to about 75–80%.Supported in part by AEC Contract No. AT(49-7)3028.