The correct spelling of the term "Expressed Sequence Tag" is phonetically transcribed as /ɪkˈsprɛst ˈsiːkwəns tæɡ/. In this term, "expressed" is pronounced as /ɪkˈsprɛst/ and refers to genes that are actively transcribed to create a functional protein. "Sequence" is pronounced as /ˈsiːkwəns/ and refers to the specific order of DNA nucleotides. "Tag" is pronounced as /tæɡ/ and refers to a short segment of DNA used for labeling or identifying a particular gene.
An Expressed Sequence Tag (EST) refers to a small fragment of a transcribed gene or RNA molecule that has been extracted and sequenced. It serves as a short and representative segment of the expressed genetic material (mRNA) within a particular cell or tissue. The purpose of generating ESTs is to gain insights into the genes that are active or expressed at a given time in an organism or a cell.
Typically, ESTs are generated using a technique called cDNA (complementary DNA) sequencing. The process starts with the isolation and reverse transcription of mRNA molecules present in the sample. This synthesis of cDNA generates a complementary version of the mRNA template. The cDNA is then cloned and sequenced, resulting in a collection of short DNA fragments, each representing a different mRNA molecule present in the sample.
ESTs play a crucial role in gene discovery and functional analysis in various areas of biological research. By compiling and analyzing a comprehensive collection of ESTs, scientists can identify and annotate genes, study alternative splice variants, assess gene expression patterns, and investigate evolutionary relationships between species. Moreover, ESTs have been instrumental in facilitating genome sequencing projects by providing information and insights on genes, their organization, and the overall intricacies of the transcriptome.
In summary, Expressed Sequence Tags are short DNA fragments representing expressed genes obtained through reverse transcription and sequencing of complementary DNA (cDNA). They aid in identifying and characterizing genes, studying their expression levels, and contributing to the understanding of the transcriptome in different organisms and tissues.