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Magazine Chapter 10: Problem 12
During \(X\) chromosome inactivation, _________. a. female cells shut down b. RNA coats a chromosome c. pigments form d. both a and b
Short Answer
Expert verified
The correct choice is d: both a and b.
Step by step solution
01
Understand the Concept
During X chromosome inactivation, one of the two X chromosomes in female mammals is randomly silenced or 'shut down' to balance the gene dosage between males (who have one X chromosome) and females (who have two). This process ensures that females do not have twice the number of X chromosome genes active compared to males.
02
Analyze the Options
We have four options: (a) female cells shut down, (b) RNA coats a chromosome, (c) pigments form, and (d) both a and b. The goal is to choose the one that correctly explains what occurs during X chromosome inactivation.
03
Eliminate Incorrect Options
Consider option (a): It suggests that female cells shut down entirely, but only the extra X chromosome is inactivated, not the whole cell. Thus, option (a) by itself is inaccurate. Option (c), concerning pigments forming, does not directly relate to the process of X chromosome inactivation, so it is incorrect.
04
Consider Correct Phenomenon
Option (b), 'RNA coats a chromosome,' describes the role of XIST RNA, which binds to and coats the X chromosome to inactivate it. This is an accurate description of part of the process involved in X chromosome inactivation. This makes option (b) valid.
05
Evaluate Combined Option
Option (d) suggests a combination of (a) and (b). Since (a) alone is incorrect, but the concept it represents (silencing an X chromosome) is part of what's happening, and (b) is correct about the mechanism (RNA coating the chromosome), option (d) meaningfully captures the whole process.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Gene Dosage
One of the key reasons for X chromosome inactivation in female mammals is to achieve balanced gene dosage. Gene dosage refers to the number of times a gene is present in a cell, and it significantly impacts how much of a gene product, like a protein, is produced.
In simple terms, if there's a difference in gene dosage, it could lead to an imbalance. For example, if an organism has too many copies of a gene, it might produce too much of the corresponding protein, which can disrupt normal biological processes.
In simple terms, if there's a difference in gene dosage, it could lead to an imbalance. For example, if an organism has too many copies of a gene, it might produce too much of the corresponding protein, which can disrupt normal biological processes.
- Males have one X chromosome, while females have two. Without X chromosome inactivation, females would produce twice the amount of X chromosome-linked gene products compared to males.
- The inactivation of one X chromosome in females equalizes the gene dosage between males and females, ensuring that both produce gene products in similar amounts from their X chromosomes.
XIST RNA
XIST RNA plays a vital role in X chromosome inactivation. XIST stands for X Inactive Specific Transcript, and it is a long non-coding RNA. Although it doesn't code for a protein, it is crucial in the regulation of the X chromosome inactivation process.
Here's how XIST RNA works:
Here's how XIST RNA works:
- XIST RNA is produced by the X chromosome that will be inactivated.
- It coats the X chromosome, turning it into a dense structure known as a Barr body.
- This coating acts as a signal to silence the genes on that X chromosome, keeping it inactive.
Female Mammals
Female mammals undergo X chromosome inactivation as a standard biological process. This mechanism is unique to them because they possess two X chromosomes. Let's explore why this is important:
These characteristics of female mammals allow them to properly manage gene expression levels from their X chromosomes, ensuring no gender-related discrepancies arise from differential gene dosage.
- In females, only one of the two X chromosomes is needed to match the gene activity level seen in males, who have only one X chromosome.
- X chromosome inactivation typically occurs randomly in cells during early development, meaning either the maternal or paternal X could be silenced.
These characteristics of female mammals allow them to properly manage gene expression levels from their X chromosomes, ensuring no gender-related discrepancies arise from differential gene dosage.
