Final answer:
To balance X-chromosome gene expression between sexes, females employ a mechanism called X inactivation, where one of the two X chromosomes is randomly inactivated in each cell. This process ensures that females and males express similar amounts of X chromosome genes, with the inactivated chromosome forming a Barr body.
Step-by-step explanation:
In both human females and males, there is a regulatory mechanism in place to ensure that the expression levels of X-chromosome genes are balanced despite the differing number of X chromosomes. This mechanism, known as X inactivation, involves the random inactivation of one X chromosome in each cell of female mammals early in development. This inactivated X chromosome condenses into a structure known as a Barr body, effectively silencing the genes on that chromosome. As a result, females, with their two X chromosomes, express a similar amount of X chromosome genes as males, who have only one X chromosome. In species such as Drosophila, the regulation of genes on the X chromosome is also critical for ensuring proper development and function, despite differences in the dosage of X chromosome gene products between males and females.
Sex-linked traits exhibit different patterns of inheritance due to their location on sex chromosomes. In the case of humans and other organisms, these traits can demonstrate how males and females manage the expression of genes located on the X chromosome. For example, in tortoiseshell cats, X inactivation leads to a patchwork of coat colors, as different X chromosomes are inactivated in different cells.