27 - Complete(full dominance and recessiveness What causes...

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Complete (full) dominance and recessiveness What causes a recessive mutant phenotype? + = wild type (dominant) allele; m = mutant (recessive) allele Haplosufficient genes only need a single copy (+/ m ) to be fully expressed and produce sufficient functional product. This is the case for fully recessive mutations , where the phenotype is only observed in homozygous recessive individuals (e.g., m / m ) ; wild type is the dominant allele (‘normal’ phenotype: +/ m or +/+)
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Mutations of haplosufficient genes are recessive A/A A/a a/a How does complete dominance work? ( A = wild type, and a = mutant). Two non-functional alleles ( a / a ) must be present to cause a mutant phenotype; one good copy is enough for wild-type function ( A / a or A / A ).
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Two types of dominant mutations What causes a dominant mutant phenotype? + = wild type allele; M = mutant (dominant) allele 1) The wild-type allele of a gene is haploin sufficient , whereby one wild-type dose (i.e., +/ M ) is not enough to achieve normal levels of function, and two wild-type alleles (+/+) are needed for wild type phenotype. Example: null mutations (either the protein is non-functional or there is no protein produced) result in only a single functional copy of the gene (e.g., for a transcription factor or enzyme) Complete (full) dominance and recessiveness
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What causes a dominant mutant phenotype? + = wild type allele; M = mutant allele 2) A dominant negative mutation produces a defective protein that binds to the wild-type polypeptide and interferes with the wild-type function. They are characterized by a dominant or semi-dominant phenotype.
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