To solve this problem, we need to understand what Expressed Sequence Tags (ESTs) refer to.$\newline$Let's analyze each option:$\newline \bullet$Option 1: Genes expressed as RNA$\newline$ - ESTs are short sub-sequences of cDNA (complementary DNA) sequences.$\newline$ - They are derived from mRNA (messenger RNA) and represent genes that are actively expressed.$\newline$ - Therefore, ESTs are indeed related to genes expressed as RNA.$\newline \bullet$Option 2: Polypeptide expression$\newline$ - Polypeptide expression refers to the synthesis of proteins from amino acids, which is not directly related to ESTs.$\newline$ - ESTs are not involved in the direct expression of polypeptides.$\newline \bullet$Option 3: DNA polymorphism$\newline$ - DNA polymorphism involves variations in DNA sequences among individuals, which is not the primary focus of ESTs.$\newline$ - ESTs are not used to study DNA polymorphisms.$\newline \bullet$Option 4: Novel DNA sequences$\newline$ - While ESTs can help identify novel genes, they are not specifically defined as novel DNA sequences.$\newline$ - ESTs are derived from known expressed genes.$\newline$Based on the analysis, the correct option is:$\newline$Option 1: Genes expressed as RNA$\newline$This corresponds to the correct option, which is Option 1.