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After Muller's classification of gene mutation, an isomorph was described as a silent point mutant with identical gene expression as the original allele. [4] [5] m/Df = m/Dp Therefore, with respect to the relationship between the original and mutated genes, one cannot talk about the effects of dominance and/or recessiveness. [4] [5] [6]
An allele [1], or allelomorph, is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. [2]Alleles can differ at a single position through single nucleotide polymorphisms (SNP), [3] but they can also have insertions and deletions of up to several thousand base pairs.
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 ...
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.
Based on the occurrence of mutation on each chromosome, we may classify mutations into three types. A wild type or homozygous non-mutated organism is one in which neither allele is mutated. A heterozygous mutation is a mutation of only one allele. A homozygous mutation is an identical mutation of both the paternal and maternal alleles.
A diploid organism is heterozygous at a gene locus when its cells contain two different alleles (one wild-type allele and one mutant allele) of a gene. [3] The cell or organism is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to a specific genotype. Heterozygous genotypes are represented by ...
If the chromosome walk proceeds through the mutant allele, the new polymorphisms will start to show increase in recombination frequency compared to the mutant phenotype. Depending on the size of the mapping population, the mutant allele can be narrowed down to a small region (<30 Kb).
Allelic heterogeneity is the phenomenon in which different mutations at the same locus lead to the same or very similar phenotypes.These allelic variations can arise as a result of natural selection processes, as a result of exogenous mutagens, genetic drift, or genetic migration.