At the beginning of this century there was a general announcement regarding the sequencing of the human genome and the genomes of many other multicellular eukaryotes. There was surprise expressed by many that the number of protein-coding sequences is much smaller than they had expected. Which of the following accounts for most of the rest? A. Non-protein-coding DNA that is transcribed into several kinds of small RNAs without biological function. B. DNA that is translated directly without being transcribed. C. Non-protein-coding DNA that is transcribed into several kinds of small RNAs with biological function. D. "Junk" DNA that serves no possible purpose. E. rRNA and tRNA coding sequences.

C) Non-protein-coding DNA that is transcribed into several kinds of small RNAs with biological function.

Explanation:

The genome of humans consists of a variety of protein-coding and non-protein coding sequences. The protein-coding sequences are the sequences which can get translated into the protein sequences.

When the genome was sequenced, it was expected that the size of these coding sequences will be larger but the sequences came to be smaller. This shows that the rest of the genome is made of the non-coding sequences.

The importance of these non-coding sequences is that they do not form the proteins but they can undergo transcription and form the variety of RNA molecules like the regulatory RNA, the ribosomal RNA and others.

Thus, Option-C is the correct answer.