AP BIOLOGY

Detailed explanation-1: -Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell.

Detailed explanation-2: -X-chromosome inactivation is the transcriptional silencing of one X chromosome in female mammalian cells that equalizes dosage of gene products from the X chromosome between XX females and XY males [1–3]. X-chromosome inactivation in the embryo proper occurs early in development.

Detailed explanation-3: -X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into a transcriptionally inactive structure called heterochromatin.

Detailed explanation-4: -X-chromosome inactivation is responsible for sex chromosome dosage compensation in females (XX), and ensures that X-chromosomal genes are not expressed at twice the levels of expression in males (XY) [1]. It occurs during early female embryonic development [2], but the exact timing in humans is still elusive.

Detailed explanation-5: -The Barr body, also sometimes called the sex chromatin, is the inactive X chromosome in female somatic cells. Human females have two X chromosomes, while males have one X and one Y.