a mechanism that equalizes the expression of genes on the X chromosomes of males and females. In mammals, one X chromosome is deactivated to form a Barr body. Dominant--- that allele which will be phenotypically expressed when present.

The phenomenon in women, who have two copies of genes on the X chromosome, of having the same level of the products of those genes as males (who have a single X chromosome). This is due to the process of inactivation of one of the X chromosomes in females (Lyonization). See Lyon's hypothesis.

The process in organisms using a chromosomal sex determination mechanism (such as XX versus XY) that allows standard structural genes on the sex chromosome to be expressed at the same levels in females and males, regardless of the number of sex chromosomes. In mammals, dosage compensation operates by maintaining only a single active X chromosome in each cell; in Drosophila, it operates by hyperactivating the male X chromosome.