Answer:
A short double-stranded RNA, one of whose strands can block gene expression
Step-by-step explanation:
SiRNA, also known as short interfering RNA, is are short double stranded DNA that binds to mRNA for the purpose of destroying the mRNA sequence, hence, preventing it from being translated into a protein.
According to this question, SiRNA can be described as a short double-stranded RNA, one of whose strands can block gene expression (translation of mRNA).