Elongation

A second remodeling protein can bind to the nucleosome...

Remodeling protein

A second remodeling protein can bind to the nucleosome...

Remodeling protein

Barr Body Microscope
| .allowing transcription without disaggregation.

14.16 Local Remodeling of Chromatin for Transcription

Initiation of transcription requires that nucleosomes disaggregate. During elongation, however, they can remain intact.

from her mother. Thus, in one embryonic cell, the paternal X might be the one remaining transcriptionally active, but in a neighboring cell, the maternal X might be active.

In the interphase cells of human females, a single, stainable nuclear body, called a Barr body after its discoverer, Murray Barr, can be seen under the light microscope (Figure 14.17). This clump of heterochromatin, which is not present in males, is the inactivated X chromosome. The number of Barr bodies in a nucleus is equal to the number of X chromosomes minus one (the one represents the X chromosome that remains transcriptionally active). So a female with the normal two X chromosomes will have one Barr body, a rare female with three X's will have two, an XXXX female will have three, and an XXY male will have one. These observations suggest that the interphase cells of each person, male or female, have a single active X chromosome, making the dosage of the expressed X chromosome genes constant across both sexes.

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Essentials of Human Physiology

Essentials of Human Physiology

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