Paramutation

From Freepedia

Paramutation, in genetics, is an interaction between two alleles of a single locus, resulting in a heritable change of one allele. Paramutation is a violation of Mendelian inheritance as one allele heritably affects the other.

Paramutation was first discovered and studied in maize (Zea mays) by R.A. Brink at the University of Wisconsin, Madison in the 1950s. Brink noticed that specific weakly expressed alleles of the red1 (r1) locus in maize, which confers red pigment to corn kernels, can heritably change specific strongly expressed alleles to a weaker expression state. The weaker expression state adopted by the changed allele is heritable and can, in turn, change the expression state of other active alleles in a process termed secondary paramutation. The weaker expression state is reversible under specific genetic conditions, suggesting that paramutation is not the result of a molecular lesion in DNA, but an epigenetic process.

Interestingly, paramutation can result in a single allele of a gene controlling a spectrum of phenotypes. At r1 in maize, for example, the weaker expression state adopted by an allele following paramutation can range from completely colorless to nearly fully-colored kernels. This is an exception to the rule that continuous varation is controlled by many genes (see multi-genic traits).

Allelic interactions similar to paramutation have since been reported in other organisms, including tomato, pea, and mouse. The molecular basis of paramutation is not known, however paramutation may share common mechanisms with other epigenetic phenomena, such as gene silencing, imprinting, and transvection (genetics).