MCD BIO CM156 Lecture Notes - Lecture 9: X-Inactivation, Barr Body, Drosophila Melanogaster
27 Jan 2020
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Some cells are making wt and others are making tabby. Barr body: little condensed staining blob in the nucleus of cells within the females. Purpose of x-inactivation: genes have to expressed at the right level, so the mechanism needs to even out gene expression within the chromosome: melanogaster: one x in male hypertranscribes, elegans: two x"s in female hypotranscribe. Most mammals: one x in females is inactivated. Some point within development, one of the x"s are inactivated then on all descendants have paternal or maternal x inactivated. Properties of the inactive x chromosome: (1) most (but not all) genes are inactivated at the transcriptional level. (2) heterochromatic (3) late replicating (4) highly methylated at cpg islands (5) histone modifications, particularly hypoacetylation. Cpg island: a sequence of at least 200 bp with a greater number of cpg sites than expected given the average cpg content of the genome. These regions are typically undermethylated and are found upstream of many mammalian genes.
