Answer:
1, Not all organisms genes contain only DNA sequence . Gene sequence in Viruses can either be DNA or RNA. Thus viral nucleic acid chains can either be single or double. Therefore the definition should have been stated as' A gene conssits of either DNA or RNA sequence that encodes a single polypeptide'' This will incorporate viral genes.
2 Basically not all genes transcribed are involved in transcription of a single polypeptide as state in the definition. Some genes specialise in ensuring that enough resources for the entire gene expression are available,E.g some ensures the adequate instruction for formation of other functional RNA molecules e,g messenger RNA,transfer RNA, needed for the stage of translation .Thus not all gene resources is concentrated on encoding a single polypeptide as implied in the question.
