Dosage compensation

Dosage Compensation

Dosage compensation is a biological mechanism that equalizes the expression of genes between males and females in species with sex chromosomes. This process ensures that both sexes have the same overall level of gene expression, despite having different sex chromosome compositions.

Mechanism

In mammals, including humans, dosage compensation is achieved by inactivating one of the two X chromosomes in females. This process, known as X chromosome inactivation, ensures that both males (XY) and females (XX) have only one active X chromosome in each cell. The inactivated X chromosome becomes a dense structure known as a Barr body.

X Chromosome Inactivation

X chromosome inactivation is initiated during early development in female embryos. The XIST gene, located on the X chromosome, produces a long non-coding RNA that coats the chromosome and recruits proteins to establish heterochromatin, leading to gene silencing. The choice of which X chromosome to inactivate is random and occurs independently in each cell, resulting in a mosaic pattern of gene expression in female tissues.

Effects

Dosage compensation ensures that genes on the X chromosome are expressed at similar levels in males and females. Without dosage compensation, females would produce twice as much protein from X-linked genes as males, leading to potential imbalances in cellular function. By equalizing gene expression, dosage compensation contributes to the overall health and development of an organism.

Clinical Implications

Disruptions in dosage compensation can lead to genetic disorders. For example, individuals with extra copies of the X chromosome (e.g., XXY in males or XXX in females) may experience dosage imbalances that result in developmental abnormalities and health issues. Understanding dosage compensation mechanisms is crucial for studying these conditions and developing potential treatments.