Question

How is the effective dosage of X-linked gene products balanced in placental mammals between females that carry two X chromosomes and males that carry only a single X chromosome?
> Genes on the single male X chromosome are expressed at twice the rate of genes on the two female X chromosomes.
> Only half of the genes on each X chromosome are expressed in female somatic cells.
>The paternally derived X chromosome is inactivated in all female somatic cells, so only the maternally derived X chromosome is expressed.
>One X chromosome is randomly inactivated in female somatic cells.

Answer 1

Answer:

One X chromosome is randomly inactivated in female somatic cells.

Explanation:

Females in placental mammals such as humans have two copies of the X chromosome while the males have only a single X chromosome in their cells.

However, the cells of males and females of these organisms have the same effective dosage of X linked genes since one of the X chromosomes in somatic cells of these females is inactivated during early embryonic stages.

The inactivated X chromosome is present in the form of a compact object, called the Barr body in the cells of the females. Methylation of DNA is considered to be the possible mechanism responsible for the inactivation of the X chromosome.