All female mammals have one active X chromosome per cell instead of two. What causes this?
a. attachment of methyl (CH3) groups to the X chromosome that will remain active
b. inactivation of the XIST gene on the X chromosome derived from the male parent
c. activation of the XIST gene on the X chromosome that will become the Barr body
d. activation of the BARR gene on one X chromosome, which then becomes inactive
Answer: c. activation of the XIST gene on the X chromosome that will become the Barr body
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Biology
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