Question

With regard to the numbers of sex chromosomes, explain why dosage compensation is necessary.

Short answer

Dosage compensation is necessary due to the differing numbers of sex chromosomes in males and females. Females have two X chromosomes, whereas males have one X and one Y chromosome. Without dosage compensation, females would produce twice as much of any given X-linked protein than males, which could potentially lead to health issues. Dosage compensation in humans is largely achieved by X-inactivation, ensuring that females, like males, have one functional copy of the X chromosome in each cell.

Step-by-step solution

Understanding Sex Chromosomes

Sex chromosomes determine an individual's sex - females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). Hence, genes that are located on these chromosomes are called sex-linked genes.

The Requirement for Dosage Compensation

Dosage compensation is the mechanism by which the differences in the number of copies of sex chromosomes are normalized, to achieve a balance in gene expression. Without dosage compensation, females, having two X chromosomes, would express twice as many proteins - a condition that could lead to overproduction of certain proteins and challenge cellular function.

Mechanism of Dosage Compensation

In humans and other mammals, dosage compensation is achieved by inactivating one of the two X chromosomes in the cells of females randomly. This process, called X inactivation or lyonization, ensures that females, like males, have one functional copy of the X chromosome in every cell.