Natural selection favors the sole expression of maternal gene copies, because it allows for the genetic coadaptation of maternal offspring traits and leads to higher offspring fitness.
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<i>A New Theory for the Evolution of Genomic Imprinting.</i> Gross L, PLoS Biology Vol. 4/12/2006, e421. <a rel="nofollow" class="external free" href="https://dx.doi.org/10.1371/journal.pbio.0040421">https://dx.doi.org/10.1371/journal.pbio.0040421</a>