PMC

Arrangement of chromosomes or chromosome arms in the spermatid nuclei from 2n = 32 heterozygotes stained with FISH. The pairs of chromosomes or chromosomal arms appear side by side in four out of six individuals (*p < 0.05)

Frequency of aneuploid spermatids in 2n = 32 heterozygotes. By FISH and specific DNA probes, the spermatid nuclei for three chromosomal pairs were examined. The Fischer test shows no significant differences between the frequency of aneuploidy for the indicated chromosomal pairs. (*p value >0.05)

Chromosome arrangement during meiotic segregation and at the spermatid nuclei. The first meiotic anaphase in a standard spermatid nucleus with the expected arrangement of two homologous Rb metacentric chromosomes (a); two pairs of homologous telocentric chromosomes (b), and one trivalent (c). The chromosomes or chromosomal arms are represented in green or red and the pericentromeric heterochromatin and the chromocenter in the spermatid nuclei is shown in blue. In the spermatid nuclei, both arms of the Rb metacentric chromosomes are expected to lie together (a′); two telocentric chromosomes should appear to be joined through their heterochromatin (b′) and the arms of the Rb chromosome or their telocentric homologs would lie together (c′)

Diagram of trivalent, options of chromosome segregation and resulting gametes. (a) Configuration of the three chromosomes in a trivalent at meiosis of a heterozygous 2n = 32. According to FISH and the specific DNA probes, one arm of the metacentric chromosome is in red (Cy2) and the other one in green (FITC) as the respective telocentric homologous chromosomes. Only one trivalent is depicted. (b) alternate segregation; (c) and (d) adjacent segregations; (b′) balanced and (b″) normal gametes; (c′), (c″), (d′), and (d″) aneuploid gametes

Chromosome in spermatids from homozygotes 2n = 40 and 2n = 24 of M. musculus domesticus. Nuclei of spermatids of individuals 2n = 40 (a–c) and 2n = 24 (d–f) are shown. In gray the homogeneous chromatin and white the central chromocenter, both stained with DAPI. Chromosomes were stained with FISH: 5, 9, and 16 are observed in red; 15, 14, and 17 in green. In a, chromosomes 5 and 15; in b, chromosomes 9 and 14; and in c, chromosomes 16 and 17. They all are connected only through the chromocenter. In contrast, in d–f, both signals corresponding to the arms of the respective Rb metacentric chromosomes are also connected through the chromocenter but now they appear side by side. Bar = 5 μm

Normal and aneuploid spermatids of Rb heterozygotes 2n = 32. Chromosomes 5, 9, and 16 in red and chromosomes 15, 14, and 17 in green were stained by FISH, while the nuclei were counterstained with DAPI. Normal or balanced spermatids with respect to chromosomes 5 and 15 (a, b), 9 and 14 (e, f), and 16 and 17 (i, j). In a, e, i, chromosomes or chromosome arms are connected together only by their heterochromatin to the chromocenter, whereas in b, f, j, chromosomes appear adjacent to each other and also connected to the chromocenter. Aneuploid spermatids: disomy of chromosome 5 (c), disomy of chromosome 15 (d); nullisomy of chromosomes 14 and 9, (g, h, respectively); nullisomy of chromosome 17 (k) and disomy of chromosome 17 (l). Bar = 5 μm