Answer: Genetic material is primarily contained in the nucleus of eukaryotic cells. Therefore, the correct answer is the nucleus. The nucleus houses the cell's DNA, which contains the genetic instructions necessary for the functioning and development of the organism. The nucleolus, on the other hand, is a substructure within the nucleus responsible for producing ribosomes. Ribosomes are cellular components involved in protein synthesis, but they do not contain the genetic material itself. The peroxisome is an organelle responsible for various metabolic processes but does not house genetic material.