Null allele: Difference between revisions
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A '''null allele''' is a mutant [[allele|copy of a gene]] at a [[locus (genetics)|locus]] that completely lacks that gene's normal function. This can be the result of the complete absence of the [[gene]] product (protein, RNA) at the molecular level, or the expression of a non-functional gene product. At the [[phenotype|phenotypic]] level, a null allele is indistinguishable from a deletion of the entire [[locus (genetics)|locus]]. |
A '''null allele''' is a mutant [[allele|copy of a gene]] at a [[locus (genetics)|locus]] that completely lacks that gene's normal function.<ref>{{Cite web|url=https://www.cancer.gov/publications/dictionaries/genetics-dictionary|title=Definition of null allele - NCI Dictionary of Cancer Terms|website=National Cancer Institute|access-date=2017-11-08}}</ref> This can be the result of the complete absence of the [[gene]] product (protein, RNA) at the molecular level, or the expression of a non-functional gene product. At the [[phenotype|phenotypic]] level, a null allele is indistinguishable from a deletion of the entire [[locus (genetics)|locus]]. |
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A mutant allele that produces no protein is called a '''protein null''' (shown by [[Western blot|western analysis]]), and one that produces no RNA is called an '''RNA null''' (shown by [[Northern blot|Northern analysis]] or by DNA sequencing of a deletion allele). A '''genetic null''' or [[Muller's morphs|amorph]]ic allele has the same phenotype when homozygous as when heterozygous with a deficiency that disrupts the locus in question. A genetic null allele can be a protein and RNA null, but can also express normal levels of a gene product that is non-functional due to mutation. |
A mutant allele that produces no protein is called a '''protein null''' (shown by [[Western blot|western analysis]]), and one that produces no RNA is called an '''RNA null''' (shown by [[Northern blot|Northern analysis]] or by DNA sequencing of a deletion allele). A '''genetic null''' or [[Muller's morphs|amorph]]ic allele has the same phenotype when homozygous as when heterozygous with a deficiency that disrupts the locus in question. A genetic null allele can be a protein and RNA null, but can also express normal levels of a gene product that is non-functional due to mutation. |
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Revision as of 03:31, 8 November 2017
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A null allele is a mutant copy of a gene at a locus that completely lacks that gene's normal function.[1] This can be the result of the complete absence of the gene product (protein, RNA) at the molecular level, or the expression of a non-functional gene product. At the phenotypic level, a null allele is indistinguishable from a deletion of the entire locus.
A mutant allele that produces no protein is called a protein null (shown by western analysis), and one that produces no RNA is called an RNA null (shown by Northern analysis or by DNA sequencing of a deletion allele). A genetic null or amorphic allele has the same phenotype when homozygous as when heterozygous with a deficiency that disrupts the locus in question. A genetic null allele can be a protein and RNA null, but can also express normal levels of a gene product that is non-functional due to mutation.
Another definition of null allele concerning molecular markers, refers to such a marker in the case it can no longer be detected because of a mutation. For example, microsatellites (i.e. a repetitive sequence of DNA, in which the repeat is rather short) are used as molecular markers amplifying them through PCR. To do so, a primer or oligonucleotide aligns with either of ends of the locus. If a mutation occurs in the annealing site, then the marker can no longer be used and the allele is turned into a null allele.
One example of a null allele is the 'O' blood type allele in the human A, B and O blood type system. The alleles for the A-antigen and B-antigen are co-dominant, thus they are both phenotypically expressed if both are present. The allele for O blood type, however, is a mutated version of the allele for the A-antigen, with a single base pair change due to genetic mutation. The protein coded for by the O allele is enzymatically inactive and therefore the O allele is expressed phenotypically in homozygous OO individuals as the lack of any blood antigen. Thus we may consider the allele for the O blood type as a null allele.
Null alleles can have lethal effects. Mice homozygous for a null allele for insulin die 48 - 72 hours after birth.[2]
See also
References
- ^ "Definition of null allele - NCI Dictionary of Cancer Terms". National Cancer Institute. Retrieved 2017-11-08.
- ^ Accili, Domenico; Drago, John; Lee, Eric; Johnson, Mark; Cool, Martha; Salvatore, Paola; Asico, Laureano; Jose, Pedro; Taylor, Simeon; Westphal, Heiner (January 12, 1996). "Early neonatal death in mice homozygous for a null allele of the insulin receptor gene". Nature Genetics. 12: 106.
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