Question: 121 Expressed Sequence Tags (ESTs) refers to
(1) All genes whether expressed or unexpressed.
(2) Certain important expressed genes.
(3) All genes that are expressed as RNA.
(4) All genes that are expressed as proteins.
Answer: Option (3)
Explanation:
Expressed Sequence Tags are short DNA sequences obtained by sequencing complementary DNA formed from messenger RNA.
Since complementary DNA is synthesized from RNA, ESTs represent only those genes that are actively expressed in a cell at a given time.
These expressed genes may code for proteins or may function as non-coding RNAs.
Therefore, ESTs correspond to all genes that are expressed as RNA and not to unexpressed genes or only protein-coding genes.
Hence, Option (3) is the correct answer.