Interspace (is) and string cob (Sg1, Sg2) as stabilizing factors for the expression of key trait genes (tr, pd)
--Walton C. Galinat
The near failure of the internodes to elongate in the cob of most modern maize (except Coroico and related corn from the Bolivian lowland of South America and Confite Morocho related corn from the highland Andes) results in an unstable expression of single vs. paired female spikelets and two ranks of spikelets vs. many ranks. Apparently with the almost side by side juxtaposition of spikelet components, small fluctuations in the internal-external environment can easily result in either a proliferation or a reduction.
Thus, in developing key trait stocks for genetic and molecular analysis, it has become necessary to include the interspace and string cob traits in the genetic background for best results.
It is significant that while the is and Sg1, Sg2 genes are now essentially absent in North American maize, they do occur in teosinte and thousands of years ago they were characteristic of the oldest maize from Tehuacan, apparently as relic remains from its teosinte origin. At that time it was carried to South America where in isolation these genes survive to this day.
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