Concepts of Genetics 11th Edition by William Klug,Michael Cummings,Charlotte Spencer,Michael Palladino

Exercise 1

A man in his early 20s received chemotherapy and radiotherapy as treatment every 60 days for Hodgkin's disease. After unsuccessful attempts to have children, he had his sperm examined at a fertility clinic, upon which multiple chromosomal irregularities were discovered. When examined within 5 days of a treatment, extra chromosomes were often present or one or more chromosomes were completely absent. However, such irregularities were not observed at day 38 or thereafter.
How might a geneticist explain the time-related differences in chromosomal irregularities?