* Genes are transcribed, not chromosomes: Chromosomes are long strands of DNA containing many genes. During transcription, only a specific segment of DNA corresponding to a single gene is copied into mRNA.
* mRNA is a messenger: mRNA's role is to carry the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm, where proteins are synthesized. If an entire chromosome was transcribed, the resulting mRNA would be too large and complex to handle, and it wouldn't be specific enough to direct protein synthesis.
* Efficiency and regulation: Transcribing only specific genes allows for efficient resource allocation and regulation. Not all genes are needed at all times, and only the necessary ones are transcribed into mRNA.
In summary: Transcription is a highly selective process. Only specific genes are transcribed into mRNA, not entire chromosomes.
