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Human male meiosis: chromosome behaviour at pre-meiotic and meiotic stages of spermatogenesis.

Normal testicular material was obtained from 53 men. The morphology and behaviour of the chromosomes during pre-meiotic and meiotic stages of spermatogenesis are described in detail. Three types of spermatogonial metaphase chromosome have been identified; they are thought to be from spermatogonia of different generations. Homologous chromosomes appear to be paired at the beginning of spermatogonial prophase, and at the onset of the meiotic prophase (leptotene). Bivalents assume a "lampbrush" appearance during mid- to late pachytene.