Reversal of dominance and wild type during the origin of maize
--Galinat, WC
The wild type generally evolves dominance in order to maintain a high frequency for its phenotype despite the presence of a load of less adaptive mutations. Under domestication and/or a switch to a new environment, certain new phenotypes may be selected as the new wild type with the old phenotypes rejected. Selection for modifying genes that would enhance the expression of the new alleles would give dominance to single dose expression, and, therefore, increase its phenotypic frequency. As the maize alleles had greater survival value under domestication than the teosinte alleles, they acquired dominance over the millennia. The maize alleles in a teosinte and primitive maize background remained as recessive.

The identity of the key maize-teosinte alleles by use of the traditional code of upper case for dominant genes and lower case for recessive genes in segregations from teosinte-modern maize hybrids can be difficult and of little value for studies of inheritance and evolution because of the mixed background of both wild and domestic modifiers of dominance.

In teosinte by primitive maize hybrids the teosinte alleles may still behave as dominants. This is the case with Rhee Flint, Coroico and possibly with Argentine popcorn. 

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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