Final answer:
In human female somatic cells, one of the two X chromosomes is selectively inactivated, a process called X chromosome inactivation, to balance gene expression between males and females. Regulatory sequences like TATA box, GC box, CAT box, enhancers, and silencers control gene expression but generally act on all gene copies, not just one chromosome copy.
Step-by-step explanation:
Regulatory Sequences and Chromosome Inactivation
Chromosomes in human female somatic cells exhibit a phenomenon known as X chromosome inactivation, where one of the two X chromosomes is silenced. This inactivation mechanism is selective, acting only on one copy of the chromosome, creating what is known as a Barr body. This process ensures that females, with their two X chromosomes, do not produce more gene products than males, who have only one X chromosome.
In eukaryotes, gene expression is largely controlled by various regulatory sequences that act as binding sites for transcription factors. These sequences include the TATA box, GC box, and CAT box, which are recognized by specific proteins necessary for activating transcription. However, it is important to note that these regulatory elements generally operate on all copies of a gene present in the cell, regardless of the chromosome.
Some regulatory sequences such as enhancers and silencers can affect gene expression in a more nuanced way. Enhancers can increase gene transcription, while silencers down-regulate or suppress it. Nonetheless, they too are not specific to a single chromosome copy; they act on any accessible copy of a gene with which they are associated.
Overall, while regulatory sequences influence gene expression at various levels, the selective inactivation of an entire chromosome, such as the X chromosome inactivation in females, acts specifically on one copy of the chromosome.