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A single-stranded RNA genome of positive polarity behaves in which way once inside a host cell?
AIt must be copied into DNA before use
BIt can act directly as viral mRNA
CIt is complementary to the viral mRNA
DIt is transcribed only in the nucleus
Answer & Solution
Correct answer: B. It can act directly as viral mRNA
1. Group IV viruses hold a single-stranded RNA genome of positive polarity.
2. Positive polarity means the genomic RNA can serve directly as mRNA, with no conversion step first.
3. Double-stranded RNA replicative intermediates are then made while copying the genome.
4. Full-length negative strands formed from those intermediates act as templates for more positive RNA.
5. Being complementary to mRNA is the definition of negative polarity, which is group V, so that option swaps the two.
6. Conversion into DNA belongs to the groups that carry reverse transcriptase, which group IV does not.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.1 Viral Evolution, Morphology, and Classification_
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