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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
Based on the solution above: A Barr body is an inactive X chromosome in the nucleus of a female cell, which ensures that females express a similar amount of X-linked genes compared to males. The process of inactivation is called X-chromosome inactivation or lyonization. The Barr body is located within the nucleus of a cell and is generally found at the periphery of the nucleus, near the nuclear envelope, as it remains condensed and is not involved in active transcription of genes.

Step by step solution

01

Define Barr body

A Barr body is an inactive X chromosome in the nucleus of a female cell. It was named after Murray Barr, a Canadian scientist who discovered it in 1949. Barr bodies are formed when one of the two X chromosomes in each female cell condenses and becomes inactive. This process of inactivation is called X-chromosome inactivation or lyonization, and it ensures that females express a similar amount of X-linked genes compared to males, who have only one X chromosome.
02

Location of Barr body in a cell

The Barr body is located within the nucleus of a cell. The nucleus is a double-membrane-bound organelle that contains the cell's genetic material (DNA). Since the Barr body is an inactive X chromosome, it is generally found at the periphery of the nucleus, near the nuclear envelope, as it remains condensed and is not involved in active transcription of genes.

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Most popular questions from this chapter

Distinguish between (a) the concepts of sexual differentiation and sex determination and (b) Protenor and Lygaeus modes of sex determination.

It is believed that any male-determining genes contained on the Y chromosome in humans are not located in the limited region that synapses with the X chromosome during meiosis. What might be the outcome if such genes were located in this region?

In this chapter, we have focused on sex differentiation, sex chro- mosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, you should answer the following fundamental questions: (a) How do we know that in humans the X chromosomes play no role in sex determination, while the Y chromosome causes maleness and its absence causes femaleness? (b) How did we originally (in the late 1940 s) analyze the sex ratio at conception in humans, and how has our approach to studying this issue changed in \(2015 ?\) (c) How do we know that \(X\) chromosomal inactivation of either the paternal or maternal homolog is a random event during early development in mammalian females? (d) How do we know that Drosophila utilizes a different sexdetermination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?

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 Drosophila, an individual female fly was observed to be of the \(\mathrm{XXY}\) chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female's father had red eyes, and the mother had white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, whiteeyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.
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