The correct answer is option 3, female somatic cells. The Barr body is a condensed, inactive X chromosome that is typically found in the nuclei of female somatic cells. It is formed during embryonic development as one of the X chromosomes in each cell becomes inactivated to achieve dosage compensation between males and females. This inactivation is random, leading to the presence of Barr bodies in different cells. The Barr body can be visualized under a microscope as a small, darkly stained body within the nucleus. It is not found in sperm, Sertoli cells, or male somatic cells. Therefore, the correct answer is option 3, female somatic cells as they are the ones that contain the Barr body.