Final answer:
A retrovirus such as HIV contains two copies of an RNA genome, known as an RNA dimer, which is reverse-transcribed into DNA once inside a host cell. Option 2, an RNA dimer, is the correct answer to what makes up the genomic component of a retrovirus particle.
Step-by-step explanation:
A retrovirus infectious particle contains an RNA dimer as its genomic component, specifically it contains two copies of the single-stranded RNA (ssRNA) genome. Retroviruses, like the Human Immunodeficiency Virus (HIV), store their genetic information in these RNA molecules. Upon entering a host cell, the viral RNA is reverse-transcribed into DNA by an enzyme called reverse transcriptase, which is produced from a viral gene. This newly synthesized DNA is then integrated into the host's genome, where it can direct the production of new viral particles.
Therefore, the correct answer to the question is: an RNA dimer, which makes option 2 the right choice. This knowledge is important for understanding how retroviruses like HIV replicate and why they can be challenging to treat.