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.
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