What is the Difference Between Expressed Sequence Tags and Sequence Annotation

The main difference between expressed sequence tags and sequence annotation is that expressed sequence tags (ESTs) are complete or partial cDNA sequences important for the confirmation of genes whereas sequence annotation is the deriving structural and functional components of a gene.

Generally, expressed sequence tags and sequence annotation are two important facts to determine structural and functional parts of the genome.

Key Areas Covered

1. What are Expressed Sequence Tags
   • Definition, Characteristics, Importance
2. What is Sequence Annotation
   • Definition, Characteristics, Importance
3. Similarities Between Expressed Sequence Tags and Sequence Annotation
   • Outline of Common Features
4. Difference Between Expressed Sequence Tags and Sequence Annotation
   • Comparison of Key Differences

Key Terms

Expressed Sequence Tags, Sequence Annotation

What are Expressed Sequence Tags

Expressed sequence tags (ESTs) are short cDNA sequences that are important in determining new genes. These expressed sequence tags are also important to identify gene transcripts. The demand for expressed sequence tags is high within the whole genome and transcriptome sequencing. An EST results from one-shot sequencing of a cloned cDNA. Generally, the cDNA for EST generation is from a single clone of a cDNA library. Moreover, ESTs represent portions of expressed genes. They are also 500-800 bp long sequences.

Figure 1: CDNA Library

Furthermore, the sequence tags of a specific chromosome are expressed by physical mapping techniques such as radiation hybrid mapping, Happy mapping, or FISH. In addition, ESTs align with the sequences of a new gene to confirm that the new gene sequence represents a gene. In general, it is a tool for the identification of genes from predicted transcripts.

What is Sequence Annotation

Sequence annotation is the process of the identification of the location of the genes or the coding regions of the genes in the genome. Once sequenced, genome annotation is important to identify the structure and function of the genome. After annotation, the genome is known with genomic position to intron-exon boundaries, regulatory sequences, repeats, gene names, and protein products. Therefore, sequence annotation allows the identification of functional elements along the genome.

Figure 2: Gene Structure

Moreover, in the last three decades, sequence annotation evolved in two aspects: the computational annotation of long protein-coding genes on single genomes and the experimental annotation of short regulatory elements. However, sequence annotation is the process of deriving the structural and functional information of a sequence.

Similarities Between Expressed Sequence Tags and Sequence Annotation

• Expressed sequence tags and sequence annotation are two important factors in identifying structural and functional parts of a genome.
• Moreover, both help in marking the elements of the genome.

Difference Between Expressed Sequence Tags and Sequence Annotation

Definition

Expressed sequence tags (ESTs) refer to the short (200–500 nucleotides) cDNA sequences that are important to identify a gene that expresses in a cell at a particular time while sequence annotation refers to the process of marking specific features in a DNA, RNA or protein sequence with descriptive information about structure or function.

Significance

Usually, expressed sequence tags are short cDNA sequences used in identifying genes while sequence annotation is the process of marking the DNA for specific structures and functions.

Function

Expressed sequence tags are important to identify new genes in the genome while sequence annotation is the process of marking DNA in the genome for genes.

Conclusion

In brief, expressed sequence tags and sequence annotation are two important factors in determining the structural and functional parts of the genome. Expressed sequence tags are short cDNA sequences that help to confirm new gene sequences in the genome, while sequence annotation is the process of marking the structural and functional parts of the genome. For example, ESTs are helpful in determining new genes in the genome. However, the main difference between expressed sequence tags and sequence annotation is their function in the genome.

References:

1. “Expressed Sequence Tag.” Expressed Sequence Tag – an Overview | ScienceDirect Topics.  
2. “Genome Annotation.” Genome Annotation – an Overview | ScienceDirect Topics.

Image Courtesy:

1. “Formation of a cDNA Library” By Dre – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Gene structure eukaryote 2 annotated” By Thomas Shafee- Own Work (CC BY 4.0) via Commons Wikimedia