Explain at least two reasons why the following definition of a gene is incomplete: ""A gene consists of DNA sequences that encode a single polypeptide.""

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.