- Sex chromatin (Barr body): a darkly stained, heterochromatic clump of chromatin subjacent to the nuclear membrane in somatic cells of normal (XX) females, representing one inactivated X chromosome.
- Lyon's hypothesis (the 'n − 1 rule'): the number of Barr bodies per cell equals the total number of X chromosomes minus one.
Formation and Structure
- During interphase, in females, one of the two X chromosomes stays uncoiled and genetically active (euchromatin), while the other becomes coiled and genetically inactive (heterochromatin), forming the Barr body.
formation of sex chromatin in a female Formation of sex chromatin in a female.