Figure 1.
Mating outcomes through inbreeding and hybridisation in one and two locus underdominance.
(A) One-locus UD A&B are mutually suppressing dominant genetic elements at the same locus. ‘Parental’ lines are either heterozygous (in blue) for both A and B alleles at the same loci (AB) or wildtype (in red) (++). Crosses between transgenic and wildtype strains (middle stream) produce F1 genotypes which carry unsuppressed lethals (A+ or B+) and are not viable. All inbreeding of wildtype (right stream) produces fully viable offspring (++). All inbreeding of AB strains (left stream) produces 50% viable offspring (AB) and 50% offspring that are homozygous at the same locus (AA or BB) and are inviable, and are highlighted in light grey (see next). For haploinsufficient RNAi, there is only one modified genetic element at the locus, ‘parental’ lines are AA only and no inviable genotypes are produced by inbreeding. In this scenario, the light grey highlighted box is viable. (B) Two-locus UD A&B are mutually suppressing unlinked dominant genetic elements, ‘parental’ lines are either homozygous for both A and B (AA,BB) or wildtype (++,++). All inbreeding of either wildtype or AA,BB strains (right and left streams, respectively) produces fully viable homozygous offspring. F1 hybrids between these strains (A+,B+) (middle stream) are also viable; however, some of the F2 progeny are non-viable. F1 hybrids therefore have reduced fitness compared with either parental homozygote. As all F1 hybrids are viable, here we illustrate crosses of these F1 hybrids to each other and both parental strains. Genotypes carrying unsuppressed lethals are highlighted in dark grey. If a single copy of a suppressor were insufficient to suppress two copies of a lethal, then these genotypes would also be inviable, these genotypes are highlighted in light grey. (C) The relationship between levels of hybridsation and fitness at the population level for interbreeding between modified populations and wildtype. Fitness is highest when individuals from either population inbreed, as the frequency of hybridisation increases, the relative fitness of the population falls.