Sex Chromatin: An Overview
Sex chromatin, also known as Barr bodies, are regions of condensed chromosome material found in all female mammalian cells. This phenomenon was first discovered in 1945 by the British geneticist and zoologist, Murray Barr. Since then, research into sex chromatin has revealed numerous biological functions, from gene expression to cellular differentiation. This article provides an overview of sex chromatin and its functions in the mammalian cell.
Structure and Function
Sex chromatin is a condensed region of the X chromosome found in female cells. It is formed through condensation of a region of the X chromosome known as the Barr body. This region is rich in heterochromatin, a type of chromatin which is highly condensed and transcriptionally inactive. The Barr body is methylated and tightly packed to form a discrete structure which can be observed during interphase of the cell cycle.
Sex chromatin is important for gene expression in the female cell. During the course of meiosis, one of the two sex chromosomes is inactivated in order to maintain gene expression balance between males and females. This is known as X chromosome inactivation, and the Barr body is the result of this process. Inactivation of the Barr body ensures that only one of the two X chromosomes is active in the female cell. This is important for ensuring proper gene expression in the female cell.
In addition to gene expression, sex chromatin has also been linked to cellular differentiation. It has been hypothesized that the Barr body may play a role in influencing the differentiation of male and female cells. This hypothesis is based on the fact that the Barr body is highly methylated, which could lead to differences in gene expression between males and females. Further research is needed to fully understand the role of the Barr body in cellular differentiation.
Conclusion
Sex chromatin, or Barr bodies, are condensed regions of heterochromatin found in female mammalian cells. These regions are important for gene expression, as they are a result of X chromosome inactivation. They have also been hypothesized to play a role in cellular differentiation, although further research is needed to fully understand this role.
References
Barr, M. L. (1945). A morphological distinction between neurones of the male and female, and its bearing on questions of cerebral evolution. Nature, 155(3935), 422–423.
Gartler, S. M. (1971). The Barr body and X-chromosome inactivation. Journal of Heredity, 62(1), 29–33.
Kouzarides, T. (2007). Chromatin modifications and their function. Cell, 128(4), 693–705.
Van den Veyver, I. B. (2016). X inactivation and the Barr body: A longstanding mystery. Endocrine Reviews, 37(2), 197–213.