Gene amplification refers to an increase in the copy of a particular gene. Here, the number of copies of a gene increases without an increase in the number of copies of other genes. There may also be an increase in the gene products, i.e. RNA and protein.
It happens naturally as well as done artificially to get the desired gene product. E.g. Multiple copies of a gene are produced in cancer cells sometimes, it occurs naturally on receiving signals from a cell or environment. Gene amplification is artificially done in a lab by polymerase chain reaction (PCR).
The piece of DNA or the gene that gets amplified naturally or artificially is known as an amplicon.
Natural Gene Amplification
The DNA is duplicated inside the cell by replication. Replication does not change the number of genes present in a cell under normal circumstances. A gene amplification naturally can occur by gene duplication. There are various ways by which gene duplication can occur naturally.
- Replication and repair slippage – An error in replication and repair leads to mutation.
- Ectopic recombination – Crossing-over between non-homologous chromosomes. It leads to chromosomal rearrangement.
- Aneuploidy and Polyploidy – Aneuploidy refers to the loss or gain of one or more chromosomes in a cell, e.g. a human cell with 45 or 47 chromosomes. Polyploidy refers to an increase in the whole set of chromosomes in a cell, e.g. triploid, hexaploid, etc.
- Retrotransposition – They are a type of transposons that copy-paste themselves at different locations through RNA intermediates.
Many tumour cells show overexpression of the amplified gene. Amplification is useful for diagnosing disease and understanding its progression. It is also a cause of developing drug resistance in cancer cells.
Artificial Gene Amplification
Artificial gene amplification is done for research, diagnosis, recombinant DNA technology and to get the desired gene product. Various ways by which gene amplification is done artificially are as follows:
- Polymerase chain reaction (PCR) – Polymerase chain reaction or PCR is commonly used to produce multiple copies of the desired gene in the lab. It requires a thermostable polymerase. The steps of polymerase chain reaction are denaturation, primer annealing and extension of primers. It is a common method for gene amplification in modern science and biotechnology. This technique is used in labs to make billions of copies of the desired gene for various purposes such as research, diagnostic and therapeutic use.
- Ligase chain reaction (LCR) – Ligase chain reaction or LCR is also a method of gene amplification. It requires a thermostable ligase as well as a polymerase. Two probes are ligated using DNA ligase, which is then amplified by PCR. It is more specific as compared to PCR. It is widely used to ascertain point mutation such as in genetic diseases.
- Transcription-mediated amplification (TMA) – This technique utilises RNA polymerase and the enzyme reverse transcriptase. Here, RNA amplicon is produced. It involves RNA transcription by RNA polymerase and DNA synthesis by reverse transcriptase. It rapidly amplifies the target gene (RNA/DNA). Multiple pathogenic organisms can be detected simultaneously in a single tube by this method.
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