Normal chiasma formation in a male with xeroderma pigmentosum

A normal chiasma count was found in first spermatocytes from one patient with the classic symptoms of the genetic disease xeroderma pigmentosum (XP). Skin fibroblasts from this patient and from a brother affected with the same disease demonstrated a decreased ability to perform DNA repair synthesis, after ultraviolet light exposure. These findings indicate that the defective enzyme in XP, probably an incision enzyme, is not involved in the process of crossing-over