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| one
of the 2 XX's
becomes transcriptionally inactive, which X is inactive seems to be randomized. During interphase in cells an inactive X-chromosome can be visualized & is called a BARR BODY. |
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| Inactivation
of X chromosome is due to
chromatin condensation via 3
mechanisms: 1. methylation (adding CH3's) on 5'Cysteine of X-chromosome DNA 2. presence of chromatin proteins that promote heterochromatinization 3. one gene on an X chromosome, when active makes an microRNA = miRISC Xist gene - makes miRISC (interference RNA) that binds to X-chromosome favoring inactivation of the X-chromosome. Once inactivated all progeny cells are also inactivated. fig of inactivation of X by RNAi* |
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How do active X-chromosomes prevent the action of siRNA? anti-Xist gene called Tsix is involved... Tsix makes an RNAi that binds complementarily to the miRNA-Xist molecule, making a double stranded RNA and thereby inactivating it. |
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end-back |
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Inactivation of normal alleles - GENE IMPRINTING* in organisms exhibiting live birth |
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