Multiple Choice
In female mammals, which X chromosome is typically inactivated during early embryonic development?
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3. Extensions to Mendelian Inheritance
X-Inactivation
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A female with a deletion of the X-inactivation center (XIC) region on one of her X chromosomes will display which of the following phenotypes?
A
The X chromosome with the XIC deletion is preferentially inactivated.
B
The X chromosome lacking the XIC cannot be inactivated, so only the normal X chromosome is inactivated.
C
Both X chromosomes are inactivated, resulting in cell lethality.
D
Both X chromosomes remain active, leading to overexpression of X-linked genes.
Verified step by step guidance1
Understand the role of the X-inactivation center (XIC): The XIC is a critical region on the X chromosome responsible for initiating X chromosome inactivation, a process that balances gene dosage between males (XY) and females (XX).
Recognize that X-inactivation is a random process in normal females, where one X chromosome is silenced to prevent overexpression of X-linked genes.
Consider what happens if one X chromosome has a deletion of the XIC: Since the XIC is necessary to start inactivation, the chromosome lacking the XIC cannot be inactivated.
Analyze the consequence: Because the X chromosome missing the XIC cannot be inactivated, the other X chromosome (with an intact XIC) must be the one that gets inactivated.
Conclude the phenotype: The female will have only the normal X chromosome inactivated, while the X chromosome lacking the XIC remains active, preventing cell lethality or overexpression from both X chromosomes.
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