EBIO 1210 Chapter Notes - Chapter 12: Triple X Syndrome, Metaphase, Fundamental Theorem Of Arithmetic
6 Mar 2016
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Most of on x chromosome in each cell in female mammals become inactivated during early embryonic development. The inactive x in each cell of a female condenses into a compact object called a barr body which lies along the nuclear envelope and is not expressed. Barr bodies are reactivated in cells that become eggs so every female gamete has an active x. Inactivation of an x chromosome involves modification of the dna and the histone proteins bound to it (methyl group ch3 to nitrogenous base) The two regions, one one each x, associate briefly with each other in each cell at an early stage of embryonic cell development. Then a gene called xist (x-inactive specific transcript) becomes active only on the chromosome that will become the barr body. Copies of the rna product of this gene attach to its origin on the x chromosome and almost cover it. Interaction of rna with the chromosome initiates inactivation.
