All female mammals have one active X chromosome per cell instead of two. What causes this?
A) activation of the XIST gene on the X chromosome that will become the Barr body
B) activation of the BARR gene on one X chromosome, which then becomes inactive
C) crossing over between the XIST gene on one X chromosome and a related gene on an autosome
D) inactivation of the XIST gene on the X chromosome derived from the male parent
E) attachment of methyl (CH3) groups to the X chromosome that will remain active

Question

Quizplus · Accepted Answer

The X-inactivation process in female mammals involves the activation of the XIST gene on one of the two X chromosomes in each cell, which leads to the production of the XIST RNA molecule. This molecule coats the X chromosome on which it is produced and triggers the condensation and inactivation of that chromosome as a Barr body. The other X chromosome remains active and is used for gene expression. Therefore, all female mammals have one active X chromosome per cell instead of two.

All Female Mammals Have One Active X Chromosome Per Cell