Association of the extra chromosome of tertiary trisomic male mice with the sex chromosomes during first meiotic prophase, and its significance for impairment of spermatogenesis.

Pachytene nuclei were studied in five tertiary trisomic male mice of Ts(1(13))70H and two of Ts(5(12))31H, with special attention given to the sex vesicles. Silver stained air dried cells analysed by light microscopy were used mainly, but in addition one sample of surface spread, ethanolic phosphotungstic acid stained nuclei was analysed by electron microscopy. With both techniques and both karyotypes, the extra chromosome (or the greater part of it) almost consistently aggregated with the sex chromosomes. Thereby, the chromatin structure of the extra chromosome as judged by a fine granular appearance resembled that of the sex chromosomes. The animals used ranged from almost azospermic to fertile oligospermic. This variation was not reflected in the position and morphology of the chromosomes 1(13) and 5(12). -Using the whole mount spreading EM technique within a Ts(1(13))70H tertiary trisomic, both 13;13;1(13) trivalents and 1(13) univalents were observed. The 13;13;1(13) trivalents showed a variety of morphologies, ranging from a situation showing classical partner exchange to complete synapsis between the two 13 homologues with the 1(13) telomeric region adhering. The latter configuration is thought not to lead to chiasma formation.