Chimeric gene
Encyclopedia
Chimeric genes form through the combination of portions of one or more coding sequences
to produce new genes. These mutation
s are distinct from fusion genes
which merge whole gene sequences into a single reading frame and often retain their original functions.
or DNA repair
so that pieces of two different genes are inadvertently combined . Chimeric genes can also form through retrotransposition
where a retrotransposon accidentally copies the transcript of a gene and inserts it into the genome in a new location. Depending on where the new retrogene appears, it can recruit new exon
s to produce a chimeric gene. Finally, ectopic recombination
, when there is an exchange between portions of the genome that are not actually related, can also produce chimeric genes. This process occurs often in human genomes, and abnormal chimeras formed by this process are known to cause color blindness
.
s, they provide a source of new genes, which can allow organisms to develop new phenotype
s and adapt
to their environment. Unlike duplicate genes, chimeric proteins are immediately distinct from their parental genes, and therefore are more likely to produce entirely new functions.
Chimeric fusion proteins form often in genomes , and many of these are likely to be dysfunctional and eliminated by natural selection. However, in some cases, these new peptides can form fully functional gene products that are selectively favored
and spread through populations quickly.
and has been named Jingwei
. This gene is formed from a retrotransposed
copy of Alcohol dehydrogenase
that united with the yellow emperor gene to produce a new protein. The new amino acid residues that it recruited from yellow emperor allow the new protein to act on long chain alcohols and diols, including growth hormones and pheremones. These changes affect fly development. In this case, the combination of different protein domains resulted in a gene that was fully functional and favored by selection.
The functions of many chimeric genes are not yet known. In some cases these gene products are not beneficial and they may even cause diseases such as cancer.
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
to produce new genes. These mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s are distinct from fusion genes
Fusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...
which merge whole gene sequences into a single reading frame and often retain their original functions.
Formation
Chimeric genes can form through several different means. Many chimeric genes form through errors in DNA replicationDNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
or DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
so that pieces of two different genes are inadvertently combined . Chimeric genes can also form through retrotransposition
Retrotransposon
Retrotransposons are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. They are a subclass of transposon. They are particularly abundant in plants, where they are often a principal component of nuclear DNA...
where a retrotransposon accidentally copies the transcript of a gene and inserts it into the genome in a new location. Depending on where the new retrogene appears, it can recruit new exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s to produce a chimeric gene. Finally, ectopic recombination
Ectopic recombination
Ectopic recombination is the recombination between sequences present at different genomic locations....
, when there is an exchange between portions of the genome that are not actually related, can also produce chimeric genes. This process occurs often in human genomes, and abnormal chimeras formed by this process are known to cause color blindness
Color blindness
Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired...
.
Evolutionary Importance of Fusion Proteins
Chimeric genes are important players in the evolution of genetic novelty. Much like gene duplicationGene duplication
Gene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome.The second copy of the gene is often free from selective pressure — that is, mutations of it have no...
s, they provide a source of new genes, which can allow organisms to develop new phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
s and adapt
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
to their environment. Unlike duplicate genes, chimeric proteins are immediately distinct from their parental genes, and therefore are more likely to produce entirely new functions.
Chimeric fusion proteins form often in genomes , and many of these are likely to be dysfunctional and eliminated by natural selection. However, in some cases, these new peptides can form fully functional gene products that are selectively favored
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
and spread through populations quickly.
Functions
One of the most well known chimeric genes was identified in DrosophilaDrosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
and has been named Jingwei
Jingwei
Jingwei is the name of a character in Chinese mythology. Originally the daughter of the emperor Yandi, she perished at a young age in the East Sea. After her death she chose to assume the shape of a bird in order to exact revenge upon the sea by bringing stones and small twigs from the mountains...
. This gene is formed from a retrotransposed
Retrotransposon
Retrotransposons are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. They are a subclass of transposon. They are particularly abundant in plants, where they are often a principal component of nuclear DNA...
copy of Alcohol dehydrogenase
Alcohol dehydrogenase
Alcohol dehydrogenases are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide...
that united with the yellow emperor gene to produce a new protein. The new amino acid residues that it recruited from yellow emperor allow the new protein to act on long chain alcohols and diols, including growth hormones and pheremones. These changes affect fly development. In this case, the combination of different protein domains resulted in a gene that was fully functional and favored by selection.
The functions of many chimeric genes are not yet known. In some cases these gene products are not beneficial and they may even cause diseases such as cancer.