In fsl¹/fsl¹ homozygotes and fsl¹/Df(3L)BK10 hemizygotes, meiotic prometaphase and metaphase I appear normal. However, in some ana-telophases, chromosome segregation is disrupted. In fsl¹/fsl¹ homozygotes and fsl¹/Df(3L)BK10 hemizygotes, meiotic metaphase II and early anaphase II, approximately 50% of cells are devoid of chromosomes. In approximately half of fsl¹/fsl¹ or fsl¹/Df(3L)BK10 mutant ana-telophase I cells, all chromosomes segregate to one pole only, leading to the formation of secondary spermatocytes that are completely devoid of chromosomes. In approximately 30.7% of fsl¹/fsl¹ mutant ana-telophase II cells, all chromosomes segregate to one pole only, leading to the formation of secondary spermatocytes that are completely devoid of chromosomes. Chromosome-containing fsl¹ secondary spermatocytes form a regular spindle and exhibit the same aberrant chromosome behaviour seen in the first meiotic division. In fsl¹ secondary spermatocytes without chromosomes, centrosomes nucleate robust astral arrays of microtubules that move to the opposite cell poles. These asters give rise to metaphase-like spindles devoid of chromosomes that differ from their wild-type counterparts only for the absence of kinetochore fibers. In these chromosome-free spindles, there is limited overlapping between the antiparallel microtubules emanating from the opposite poles. However, little or no overlapping of these microtubules is also seen in wild-type metaphase spindles. Chromosome-free spindles evolve into an anaphase A-like configuration, which displays little or no microtubule overlapping at the center of the cell, as occurs in wild-type anaphases. These anaphase A-like spindles undergo anaphase B, assemble a morphologically normal central spindle, and elongate to form telophase figures that are indistinguishable from their wild-type counterparts. In fsl¹ mutants, some nebenkern are not associated with nuclei.