An inactivated X chromosome, found in somatic cells of female mammals, manifests as a condensed structure within the nucleus. This structure represents a mechanism of dosage compensation, ensuring that females, with two X chromosomes, do not produce twice as many X-linked gene products as males, who possess only one X chromosome. For instance, in human females, one X chromosome randomly undergoes inactivation early in embryonic development, forming this observable entity.
The discovery of this chromatin body was pivotal in understanding sex chromosome aneuploidies, such as Turner syndrome (XO) and Klinefelter syndrome (XXY). Its presence or absence can be used diagnostically to determine genetic sex and identify chromosomal abnormalities. Historically, its identification provided significant insights into gene regulation and the role of chromosomes in development and disease.
