Severe morphological alterations in the midpiece of developing and mature sperm.
A, transmission electron microscopy showed an increase in swollen mitochondria in late spermatids (testis) and epididymal spermatozoa (arrows). B, scanning electron microscopy of isolated sperm revealed severe morphological aberrations in the midpiece and the midpiece-principal piece junction of heterozygous spermatozoa (scale bar: A, 2 μm, insets = 200 nm; B, 10 μm, insets = 1 μm).