Blm^cko/neo spermatocytes show defects in synapsis. Pachytene spermatocytes from Blm^cko/neo mice stained with antibodies against synaptonemal complex proteins SYCP3 (red) and SYCP1 (green). Chromosomes displaying defective synapsis are shown by asterisks and in corresponding insets. Unsynapsed chromosomes that accumulate SYCP3 at the axial elements but not SYCP1 in the central element are shown by white arrows. Defective pairing, causing complex chromosome configurations not seen in wild-type pachynema, also occurs in Blm^cko/neo (gray arrows). A cartoon is provided as a simple interpretation of this complex configuration, although other interpretations are also possible.