Final answer:
If a recently fertilized ovum is exposed to 25 rad, it is likely to experience chromosomal damage due to the high sensitivity of rapidly dividing embryonic cells to radiation. This can lead to somatic or genetic damage and serious developmental defects or miscarriage.
Step-by-step explanation:
If 25 rad is accidentally delivered to a recently fertilized ovum, possible chromosomal damage is likely to occur. This level of radiation can have detrimental effects on rapidly dividing cells, which include the cells of an embryo. The sensitivity of embryos to radiation means particular care is necessary to avoid exposure during pregnancy due to the risk of somatic damage or genetic damage.
Exposure to even relatively low doses of radiation can result in a range of adverse effects including the temporary suppression of the immune system, reduction in white blood cell count, and potentially more serious outcomes such as sterility or fatal damage depending on the dose received. Furthermore, the developing embryo may suffer severe consequences, potentially leading to miscarriage or significant developmental defects.