Women (and all female mammals) have one active X chromosome per ...

[Hungry!]

Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?
A) modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive
B) activation of the Barr gene on one of the two X chromosomes that then inactivates
C) crossover 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) the removal of methyl (CH3) groups from the X chromosome that will remain active

[camila]

100% it's A, don't forget to gimmi a thumbs up

[Hungry!]

Thanks so much, you were right on.