Multiple Choice
All female mammals have one active X chromosome per cell instead of two. What causes this phenomenon?
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3. Extensions to Mendelian Inheritance
X-Inactivation
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If two X chromosomes are present in a mammalian cell, one of them is converted to a(n):
A
nucleolus
B
Barr body
C
chromatid
D
centromere
Verified step by step guidance1
Understand that in mammalian females, which have two X chromosomes (XX), one of the X chromosomes undergoes a process called X-inactivation to balance gene expression with males (XY).
Recognize that the inactivated X chromosome condenses into a dense, compact structure within the nucleus, which is visible under a microscope.
Identify this condensed structure as the Barr body, named after the scientist who discovered it.
Recall that the Barr body is not a nucleolus, chromatid, or centromere, but specifically the inactivated X chromosome.
Conclude that when two X chromosomes are present, one is converted into a Barr body to ensure dosage compensation in gene expression.
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