BME 80H Lecture Notes - Lecture 22: Murray Barr, Dosage Compensation, Tortoiseshell
11 Jun 2018
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Lecture 22
III. Dosage compensation and X-inactivation
A. X Inactivation: inactivation of one of the 2 X chromosomes
in somatic cells of females (fig. 7.16-7.19)
1. Barr Body (Murray Barr, 1949) (figure 7.16)
2. Dosage compensation and the Lyon Hypothesis
(Mary Lyon, 1961)
- Observed coat color in mice and found the Barr Body
to be an inactivated X chromosome
- Female mice, heterozygous for an X-linked coat color
gene had patches of two different colors
- Males all had even coloration
3. Females heterozygotic for X-linked genes contain cells that differ
in their phenotypes with respect to expression of these genes
(figure 7.17).
- Female has patches of cells representing expression
of one or the other X chromosome
- Tortoise shell cat has patches of orange and black Xo
and Xb (o and b should be superscript)
- One or the other is inactivated in certain places
4. X-inactivation and development (figure 7.18,
Handout: figure 6.11 HG 5th)
- Occurs early in development, after fertilization
- Example of epigenetics
- Which X is inactivated is random
- Once a cell has an X inactivated all the descendent
cells also don’t have that X
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Document Summary
Dosage compensation and x-inactivation: x inactivation: inactivation of one of the 2 x chromosomes in somatic cells of females (fig. 7. 16-7. 19: barr body (murray barr, 1949) (figure 7. 16, dosage compensation and the lyon hypothesis (mary lyon, 1961) Observed coat color in mice and found the barr body to be an inactivated x chromosome. Female mice, heterozygous for an x-linked coat color gene had patches of two different colors. Males all had even coloration: females heterozygotic for x-linked genes contain cells that differ in their phenotypes with respect to expression of these genes (figure 7. 17). Female has patches of cells representing expression of one or the other x chromosome. Tortoise shell cat has patches of orange and black xo and xb (o and b should be superscript) One or the other is inactivated in certain places: x-inactivation and development (figure 7. 18, Once a cell has an x inactivated all the descendent cells also don t have that x.
