Final answer:
RNA phages commonly contain single-stranded RNA (+ssRNA) as their genome, which can directly serve as mRNA for protein synthesis.
Step-by-step explanation:
The student has asked which type of genetic material RNA phages usually contain. RNA phages are known to have a genome that consists of RNA, rather than DNA, but the question requires specifying the form of this RNA. Based on the Baltimore classification scheme, RNA phages typically contain single-stranded RNA (ssRNA) as their genome. More specifically, these phages generally contain positive polarity single-strand RNA (+ssRNA), which means that the genomic RNA can serve directly as mRNA. The +ssRNA is therefore immediately available for translation to produce viral proteins. In contrast, double-stranded RNA (dsRNA), double-stranded DNA (dsDNA), and single-stranded DNA (ssDNA) each require additional steps before they can be used in protein synthesis.