Schematic illustration of the classic definition of different gene actions for a biallelic, locus “X” with homozygote genotypes “aa” (the recessive alleles) and “AA” (the dominant alleles), and heterozygote genotype “Aa” (hybrid).

<p>A: additive gene action, B: complete dominance gene action that causes the same values for both dominant heterozygote and homozygote individuals, C: partial dominance gene action, D: overdominance gene action, E: gene actions based on the genetic ratio (<i>GR</i>) values, F: gene actions based on the <i>DH</i> values, G: additive and dominance gene actions described by Gjuvsland et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087034#pone.0087034-SAS1" target="_blank">[45]</a> (doi:10.1371/journal.pone.0009379.g001), the blue accolade (<i>nd</i> area) and the red accolade (<i>pd</i> area) have been added to the original version of the image, H: gene actions based on the Petr and Frey (1966), and Falconer (1989) formulas. <i>a</i>: additive, <i>na</i>: non-additive, <i>d</i>: dominance, <i>nd</i>: negative dominance, <i>cd</i>: complete or full dominance, <i>cr</i>: complete of full recessive, <i>pd</i>: partial dominance, <i>pr</i>: partial recessive, <i>od</i>: overdominance.