Biology 1202B Lecture Notes - Lecture 15: Epigenome, Barr Body, Chromosome
Document Summary
Histones are modified by methylation, acetylation, phosphorylation, and other modifications. Combinations of specific histone modifications define the function of local regions of chromatin. Hp1 is the key protein in forming mammalian heterochromatin, and acts by binding to methylated histone h3. Dosage compensation mechanisms employed to compensate for the discrepancy between the presence of two x chromosomes in one sex but only one x chromosome in other sex. In female mammals, they will shut down one of their x chromosomes, making it equal. Cell still has 2x chromosomes active until cell inactives one. All descendants will keep the same x active. Happens at a very early stage in cell development. Regions on body which are descended from one particular cell which deactivate one x chromosome. Leads to heterochromatic x chromosome and barr body. Situations with abnormal x chromosome count ie: xxy male, xxx female.