Final answer:
Barr bodies are seen in individuals with more than one X chromosome, typically in females (XX) and males with Klinefelter syndrome (XXY). They are not found in typical males (XY) or those with Turner syndrome (XO).
Step-by-step explanation:
In mammals, sex determination is typically characterized by XX chromosomes for females and XY for males. Female mammals have two X chromosomes, but only one is active in any given cell. The inactive X chromosome condenses to form what is known as a Barr body. This process ensures that females, like males, have only one functional copy of the X chromosome in each body cell, preventing an overdose of X-linked gene expression. Therefore, a Barr body is typically indicative of the second X chromosome in females (XX genotype) and is not present in typical male cells (XY genotype).
However, in some genetic conditions such as Klinefelter syndrome (XXY), the individual is phenotypically male but has an extra X chromosome. In this case, one of the X chromosomes will form a Barr body due to the same inactivation process that occurs in females. This means that Barr bodies can also be observed in individuals with Klinefelter syndrome due to their XXY genotype.
Conversely, individuals with Turner syndrome (XO) will not have a Barr body since they only possess a single X chromosome with no additional X to inactivate.