Comment Re:Only makes sense if... (Score 2) 96
Yes it still gives redundancy for at least two reasons.
1) Even on the Barr-body, some genes are expressed (XCI escape genes).
2) Also, it is not the same X-chrome in every cell that is inactivated: Selection of the X-chromosome to be inactivated happens early but there's still multiple cells making the choice independently - so the body effectively consists of a mix of cells with one X activated in some cells, and the other in others. This can be enough to overcome some genetic disorders like haemophilia caused by a passed down mutated X-chromosome gene: because as long as (roughly) half the cells in the liver have the good version activated, it is enough to prevent blood clotting etc.