Opaque-2 mutant

For years, plant scientists assayed the world s corn varieties one by one, looking for a strain with more nutritionally balanced protein. Finally, in 1963, a Purdue University team headed by biochemist Edwin T. Mertz analyzed an odd group of corns characterized by soft, floury endosperm inside an opaque, chalk-white kernel. The Purdue scientists found that the opaque characteristic of corn, which had been noted for years without exciting much scientific interest, is associated with a recessive gene that replaces some of the kernel s amino acid deficient zein with other protein higher in the needed lysine and tryptophan. The mutant— routinely labeled opaque-2, or O2 for short—had a lysine... 

In the new mutant corn, opaque-2, the ratio between the protein fractions is changed, with the zein content lowered from about 50% to less than 30% of the protein. The net result of this changed ratio is that opaque-2 has a higher content of lysine and tryptophan than regular corn. For this reason, corn of this type can supply a larger part of the protein requirement in the diets of people than ordinary corn. 

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