Transheterozygote
Encyclopedia
The term transheterozygote is used in modern genetics periodicals in two different ways. In the first, the transheterozygote has one mutant (-) and one wildtype allele (+) at each of two different genes (A-/A+ and B-/B+ where A and B are different genes). In the second, the transheterozygote carries two different mutated alleles of the same gene (A*/A', see example below). This second definition also applies to the term "heteroallelic combination".
Organisms with one mutant and one wildtype allele at one locus are called simply heterozygous, not transheterozygous.
Transheterozygotes are useful in the study of genetic interactions
and complementation
testing.
(genes). Each of the two loci has one natural (or wild type
) allele and one allele
that differs from the natural allele because of a mutation
. Such an organism can be created by crossing together two organisms that carry one mutation each, in two different genes, and selecting for the presence of both mutations simultaneously in an individual offspring. The offspring will have one mutant allele and one wildtype allele at each of the two genes being studied.
Transheterozygotes are useful in the study of genetic interactions
. An example from Drosophila
research: the wing vein phenotype of a recessive mutation in the Epidermal growth factor receptor (Egfr), a gene required for communication between cells, can be dominantly enhanced by a recessive mutation in Notch, another cell-signalling gene. A transheterozygote between Egfr and Notch has the genotype Notch/+ ; Egfr/+ (where Notch and Egfr represent mutant alleles, and + represents wildtype alleles). The dominant interaction between Egfr and Notch suggested that the Egfr and Notch signalling pathways act together within the cell to affect the pattern of veins in the fly's wings.
s are different mutated
versions of the normal (or wild type
) allele. The presence of two different mutant alleles at the same locus are often referred to as a heteroallelic combination.
A transheterozygous (heteroallelic) organism can be created by first crossing together two mutants, each with a different mutation affecting the same locus, and screening for the presence of both alleles simultaneously in an individual offspring. A recent research paper using this definition reported cases of transvection
between different alleles of Hsp90.
This second definition is also sometimes applied to the situation where two different chromosomal deletions exist in trans (on the different homologous chromosomes) and fail to complement because they disrupt one or more common genes. (For example, Df(E1)/Df(GN50) in Stowers, et al. 2000).
By way of example, transheterozygote (heteroallelic combination) can result from a cross between two organisms with genotype
s AA* and AA', where A is the wild type allele of a given gene, and A* and A' are two different mutant alleles of that gene. As can be seen in the following Punnett square
, approximately one fourth of the offspring of this cross will inherit both the A* and A' mutant alleles, resulting in a transheterozygote genotype of A*A'.
Transheterozygotes are useful in complementation
testing, as pioneered by geneticist
Edward B. Lewis
. If a transheterozygote inheriting two unknown recessive
mutations continues to show the mutant phenotype
, it can be concluded that both mutations must be in the same gene
, because inheritance of just one recessive mutation in each of two different genes would result in an organism displaying the dominant wild type phenotype.
Organisms with one mutant and one wildtype allele at one locus are called simply heterozygous, not transheterozygous.
Transheterozygotes are useful in the study of genetic interactions
Epistasis
In genetics, epistasis is the phenomenon where the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is called epistatic, while the phenotype altered or suppressed is called hypostatic...
and complementation
Complementation (genetics)
In genetics, complementation refers to a relationship between two different strains of an organism which both have homozygous recessive mutations that produce the same phenotype . These strains are true breeding for their mutation...
testing.
Transheterozygous at two loci
A transheterozygote is a diploid organism that is heterozygous at two different lociLocus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
(genes). Each of the two loci has one natural (or wild type
Wild type
Wild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
) allele and one allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
that differs from the natural allele because of a 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...
. Such an organism can be created by crossing together two organisms that carry one mutation each, in two different genes, and selecting for the presence of both mutations simultaneously in an individual offspring. The offspring will have one mutant allele and one wildtype allele at each of the two genes being studied.
Transheterozygotes are useful in the study of genetic interactions
Epistasis
In genetics, epistasis is the phenomenon where the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is called epistatic, while the phenotype altered or suppressed is called hypostatic...
. An example from Drosophila
Drosophila
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...
research: the wing vein phenotype of a recessive mutation in the Epidermal growth factor receptor (Egfr), a gene required for communication between cells, can be dominantly enhanced by a recessive mutation in Notch, another cell-signalling gene. A transheterozygote between Egfr and Notch has the genotype Notch/+ ; Egfr/+ (where Notch and Egfr represent mutant alleles, and + represents wildtype alleles). The dominant interaction between Egfr and Notch suggested that the Egfr and Notch signalling pathways act together within the cell to affect the pattern of veins in the fly's wings.
Heteroallelic combination at one locus
Transheterozygote refers to a diploid organism for which both alleleAllele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s are different mutated
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...
versions of the normal (or wild type
Wild type
Wild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
) allele. The presence of two different mutant alleles at the same locus are often referred to as a heteroallelic combination.
A transheterozygous (heteroallelic) organism can be created by first crossing together two mutants, each with a different mutation affecting the same locus, and screening for the presence of both alleles simultaneously in an individual offspring. A recent research paper using this definition reported cases of transvection
Transvection
Transvection may refer to:*Transvection *Transvection *Transvection...
between different alleles of Hsp90.
This second definition is also sometimes applied to the situation where two different chromosomal deletions exist in trans (on the different homologous chromosomes) and fail to complement because they disrupt one or more common genes. (For example, Df(E1)/Df(GN50) in Stowers, et al. 2000).
By way of example, transheterozygote (heteroallelic combination) can result from a cross between two organisms with genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
s AA* and AA', where A is the wild type allele of a given gene, and A* and A' are two different mutant alleles of that gene. As can be seen in the following Punnett square
Punnett square
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach, and is used by biologists to determine the probability of an offspring's having a particular genotype...
, approximately one fourth of the offspring of this cross will inherit both the A* and A' mutant alleles, resulting in a transheterozygote genotype of A*A'.
| A | A* | |
|---|---|---|
| A | A A | A A* |
| A' | A A' | A* A' |
Transheterozygotes are useful in complementation
Complementation (genetics)
In genetics, complementation refers to a relationship between two different strains of an organism which both have homozygous recessive mutations that produce the same phenotype . These strains are true breeding for their mutation...
testing, as pioneered by geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
Edward B. Lewis
Edward B. Lewis
- External links :* *...
. If a transheterozygote inheriting two unknown recessive
Recessive
In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...
mutations continues to show the mutant 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...
, it can be concluded that both mutations must be in the same gene
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...
, because inheritance of just one recessive mutation in each of two different genes would result in an organism displaying the dominant wild type phenotype.
External links
- Genetic dissection of biochemical pathways, Prof. Sharon Amacher, UC Berkeley