Multiple Choice
If two X chromosomes are present in a mammalian cell, one of them is converted to a(n):
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3. Extensions to Mendelian Inheritance
X-Inactivation
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In female mammals, which X chromosome is typically inactivated during early embryonic development?
A
Only the maternal X chromosome is always inactivated
B
Either the maternal or paternal X chromosome, chosen at random in each cell
C
Only the paternal X chromosome is always inactivated
D
Both X chromosomes are inactivated in every cell
Verified step by step guidance1
Understand the concept of X chromosome inactivation (XCI), which is a process in female mammals to balance gene dosage between XX females and XY males by inactivating one of the two X chromosomes in each cell.
Recognize that XCI occurs early in embryonic development and that it is a random process in most female mammals, meaning either the maternal or paternal X chromosome can be inactivated in each individual cell.
Note that once an X chromosome is inactivated in a cell, all daughter cells derived from that cell will maintain the same inactive X chromosome, leading to a mosaic pattern of X chromosome expression.
Eliminate options stating that only the maternal or only the paternal X chromosome is always inactivated, as this is not the case in typical random XCI.
Conclude that the correct understanding is that either the maternal or paternal X chromosome is chosen at random for inactivation in each cell during early embryonic development.
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