Final answer:
X-inactive specific transcript (XIST) is an IncRNA that forms Barr bodies during X inactivation in female mammals. The inactive X chromosome does not express its genes, compensating for the double genetic dose in females.
Step-by-step explanation:
X-inactive specific transcript (XIST) is a recently discovered IncRNA that plays a crucial role in the process of X inactivation in female mammals. XIST is required to form Barr bodies, which are condensed structures that form when one of the X chromosomes in somatic cells is inactivated. The genes on the inactive X chromosome are not expressed, allowing females to compensate for their double genetic dose of X chromosome.