Mutable genes

Chopra, S. et al.. Excision of the Candystripel transposon from a hyper-mutable Yl-cs allele shows that the sorghum Y1 gene controls the biosynthesis of both 3-deoxyanthocyanidin phytoalexins and phlobaphene pigments. Physiol. Mol. Plant Pathol., 60, 321, 2002. 

Figure 40-4 Schematic representation of the polygiutamine-encoding CAG repeat in exon 1 of the HD gene and associated alleles. A CAG-repeat number <27 is considered normal. CAG-repeat numbers of 28 to 35 are mutable" and although they are not associated with an abnormal phenotype, these alleles are prone to meiotic expansion to an HD allele. CAG repeats of 36 to 39 are considered HD alleles but with reduced penetrance, indicating that both unaffected and affected patients have been reported with alleles of this size, CAG repeats >40 are associated with HD with complete penetrance.

An analysis of mutable sites in the DNA-binding domain of human p53 has been performed using a yeast functional assay. This assay is based on the expression of human p53 introduced into Saccharomyces cerevisiae containing a p53-dependent reporter gene. Random mutagenesis has revealed that mutation at 542 sites in a 1079-bp fragment could inactivate p53 DNA binding. This number is remarkably close to the number of observed sites at... 

Roush, A. A., Suarez, M., Friedberg, E. C., Radman, M., and Siede, W. (1998). Deletion of the Saccharomyces cerevisiae gene RAD30 encoding an Escherichia coli DinB homolog confers UV radiation sensitivity and altered mutability. Mol. Gen. Genet. 257, 686-692. 

Hundreds of loci are involved in the barley chlorophyll mutation system (Gustafsson, 1955), and tests for sterility in barley, embryonic lethals in Arabidopsis, or quantitative traits in different species probably respond to mutations in thousands of loci. These tests record forward mutation independently of locus specificities inferred from variations in phenotype spectra and from mutabilities of individual genes cf. Ehrenberg et al., 1956 Lundqvist et al., 1968). 

The presence of unstable loci has been demonstrated, their high mutability, however, depending not on changes in themselves, but on the presence of the controller gene. 

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