Data from: A dominance hypothesis argument for historical genetic gains and the fixation of heterosis in octoploid strawberry

Heterosis was the catalyst for the domestication of cultivated strawberry
(Fragaria × ananassa), an interspecific hybrid species that originated in
the 1700s.  The hybrid origin was discovered because the
phenotypes of spontaneous hybrids transgressed those of their parent
species.  The transgressions included fruit yield increases and
other genetic gains in the twentieth century that sparked the global
expansion of strawberry production.  The importance of heterosis
to the agricultural success of the hybrid species, however, has remained a
mystery.  Here we show that heterosis has disappeared (become
fixed) among improved hybrids within a population (the California
population) that has been under long-term selection for increased fruit
yield, weight, and firmness.  We found that the highest yielding
hybrids are among the most highly inbred (59-79%), which seems
counterintuitive for a highly heterozygous, outbreeder carrying heavy
genetic loads.  Although faint remnants of heterosis were
discovered, the between-parent allele frequency differences and dispersed
favorable dominant alleles necessary for heterosis have decreased nearly
genome-wide within the California population.  Conversely,
heterosis was prevalent and significant among wide hybrids, especially for
fruit count, a significant driver of genetic gains for fruit yield.
 We attributed the disappearance (fixation) of heterosis within
the California population to increased homozygosity of favorable dominant
alleles and inbreeding associated with selection, random genetic drift,
and selective sweeps.  Despite historical inbreeding, the highest
yielding hybrids reported to-date are estimated to be heterozygous for
20,370-44,280 of the estimated 97,000-108,000 genes in the octoploid
genome, the equivalent of an entire diploid genome or more.