Where do genetic effects of radiation primarily occur?

The genetic effects of radiation primarily occur in the germ cells, specifically in the sperm and eggs. This is because these cells carry the genetic information that can be passed down to future generations. When radiation interacts with germ cells, it can cause mutations in the DNA, which may be transmitted to offspring. If these mutations occur before fertilization, they can affect the development and health of the resulting fetus, leading to potential genetic disorders or malformations.

In contrast, the other options do not primarily concern genetic effects, as they focus on somatic tissues. For instance, while the brain and spinal cord, skin and muscle, and blood and liver can be affected by radiation, these tissues do not pass genetic changes to the next generation. Instead, the alterations in these tissues lead to somatic effects rather than hereditary changes. Thus, the correct answer focuses on the cell types that directly contribute to genetic material passed on to offspring.