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Chapter 5: Problem 16

What is a Barr body, and where is it found in a cell?

Short Answer

Expert verified
Answer: A Barr body is an inactivated X chromosome present in the nuclei of female somatic cells. It forms as a result of X-chromosome inactivation during early development to ensure proper gene expression dosage. Barr bodies are found within the cell nucleus, usually attached to the nuclear envelope.

Step by step solution

01

Define Barr Body

A Barr body, also known as a sex chromatin, is an inactivated X chromosome present in the nuclei of female somatic cells. It appears as a dense, compact structure under a microscope, consisting of heterochromatin.
02

Explain the Formation of Barr Bodies

Barr bodies form during early development as a result of a process called X-chromosome inactivation (XCI). In female mammals, one of the two X chromosomes in each cell is randomly inactivated to ensure the proper dosage of X-linked gene expression in females (XX) and males (XY). The inactive X chromosome condenses into a small, dense structure called a Barr body.
03

Describe the Location of Barr Bodies

Barr bodies are found within the nucleus of the cell, usually attached to the nuclear envelope. The nuclear envelope is a double-membrane structure that separates the nucleus from the cytoplasm and provides a boundary for the cell's genetic material. Since one X chromosome is inactivated during XCI, only one Barr body is present in most female somatic cells.

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Most popular questions from this chapter

As related to sex determination, what is meant by (a) homomorphic and heteromorphic chromosomes; and (b) homogametic sex and heterogametic sex?

An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the \(F_{1}\) and \(F_{2}\) generations from a cross between a female with reduced wings and a male with normalsized wings when (a) the female is the heterogametic sex. (b) the male is the heterogametic sex.

How do mammals, including humans, solve the "dosage problem" caused by the presence of an \(\mathrm{X}\) and \(\mathrm{Y}\) chromosome in one sex and two X chromosomes in the other sex?

Can the Lyon hypothesis be tested in a human female who is homozygous for one allele of the X-linked G6PD gene? Why, or why not?

In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the \(T f m\) allele on the \(X\) chromosome develops testes, but no further male differentiation occurs-the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and \(Y\) chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can "genetically engineer" the chromosomes of mice, to test and confirm your explanation?
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