A strong possibility to account for the observed gene-copy
silencing would be the occurrence of genomic imprinting
[9, 10], implying that gene expression control would be mediated
specifically by one parental genome, whereas copies inherited
from the other parent would be silenced in the hybrid.
This idea would be supported by the possibility of occurrence
of imprinting effects in fish, as demonstrated in inheritance of
zebrafish transgenes [11]. However, our results do not seem to
fit the expectations of a parental imprinting process [12]. In the
case of a general imprinting mechanism, single-genome-mediated
expression should be observed for the same gene in
all organs in triploid hybrids, according to the parental origin
of genomes. However, the actin gene analyzed here clearly
showed organ-specific differences in allelic expression.