The
Q
gene encodes an
AP2
-like transcription factor that played an important role in domestication of polyploid wheat. The chromosome 5A
Q
alleles (
5AQ
and
5Aq
) have been well studied, but much less is known about the
q
alleles on wheat homoeologous chromosomes 5B (
5Bq
) and 5D (
5Dq
). We investigated the organization, evolution, and function of the
Q/q
homoeoalleles in hexaploid wheat (
Triticum aestivum
L.).
Q/q
gene sequences are highly conserved within and among the A, B, and D genomes of hexaploid wheat, the A and B genomes of tetraploid wheat, and the A, S, and D genomes of the diploid progenitors, but the intergenic regions of the
Q/q
locus are highly divergent among homoeologous genomes. Duplication of the
q
gene 5.8 Mya was likely followed by selective loss of one of the copies from the A genome progenitor and the other copy from the B, D, and S genomes. A recent V
329
-to-I mutation in the A lineage is correlated with the
Q
phenotype. The
5Bq
homoeoalleles became a pseudogene after allotetraploidization. Expression analysis indicated that the homoeoalleles are coregulated in a complex manner. Combined phenotypic and expression analysis indicated that, whereas
5AQ
plays a major role in conferring domestication-related traits,
5Dq
contributes directly and
5Bq
indirectly to suppression of the speltoid phenotype. The evolution of the
Q/q
loci in polyploid wheat resulted in the hyperfunctionalization of
5AQ
, pseudogenization of
5Bq
, and subfunctionalization of
5Dq
, all contributing to the domestication traits.