In Humans and Other Mammals, X-Inactivation Takes Place

Question

In humans and other mammals, X-inactivation takes place:
A)early in development, with each new cell inheriting the same inactivated X chromosome as its parent cell.
B)late in development, with each new cell inheriting the same inactivated X chromosome as its parent cell.
C)throughout the lifetime of an organism-with each new cell division, both X chromosomes are activated, and one is then inactivated in each new cell.
D)early in development, with all maternal X chromosomes being inactivated and cells maintaining active copies of only the paternal X chromosome.
E)early in development, with all paternal X chromosomes being inactivated and cells maintaining active copies of only the maternal X chromosome.

Accepted Answer

X-inactivation takes place early in development, with each new cell inheriting the same inactivated X chromosome as its parent cell. This process ensures that female mammals, who have two X chromosomes, do not produce twice as many X chromosome gene products as male mammals, who only have one X chromosome.