A pericentric inversion in chromosome 1 of a severely oligospermic human male is reported. Pachytene analysis in microspread preparations shows an absence of full loop formation in the inversion bivalent and only the rare occurrence of a partial loop. The majority of cells exhibit extensive asynapsis across the inverted segment, or a normal looking synaptonemal complex indicative of heterologous pairing along the length of the inversion. Crossing over is reduced in the No 1 bivalent with only a rare chiasma being seen in the inverted region at metaphase I. Males heterozygous for a pericentric inversion in chromosome 1 appear to be at severe risk for infertility brought about by spermatogenic disturbance. The dearth of full loops at prophase in this patient, and in other pericentric inversion cases studied both in man and other species, raises the question of whether recombinant offspring might be rarer than anticipated on a theoretical basis owing to asynapsis or early heterologous synapsis across inverted segments.
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