Sex Determination: Sterility Genes out of Sequence John R. Pannell, Jörn Gerchen  Current Biology  Volume 28, Issue 2, Pages R80-R83 (January 2018) DOI: 10.1016/j.cub.2017.11.052 Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 1 Evolution of dioecy through the canonical two-locus model in garden asparagus. (A) Two functional copies of an autosomal gene (green circle), essential for male function (aspTDF1), are present in the hermaphrodite ancestor. (B) A loss-of-function mutation disrupts one copy (red circle). (C) Segregation of the loss-of-function mutation results in females when homozygous. (D) A dominant female function surpressor (SOFF, blue circle) is duplicated and inserted close to the functional copy of aspTDF1. Individuals with this proto-Y chromosome are male, but recombination between both sterility loci can result in neuters (sterile in both functions) or fertile hermaphrodites. (E) Selection against neuters and hermaphrodites favours recombination suppression (purple area) on the Y chromosome. (F) Previously neutral loci (small grey circles) gain sexually antagonistic function, or are translocated to the sex-determining regions (SDR, small violet circles). (G) Sexually antagonistic selection can result in extension of the non-recombining region to link sexually antagonistic loci to the SDR. Current Biology 2018 28, R80-R83DOI: (10.1016/j.cub.2017.11.052) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 2 Crossing scheme to test the dominant suppression of female function of the gene SOFF. A spontaneous mutation (red cross) that disrupts the dominant suppressor of female function, SOFF (blue circle) are self-fertilized (or crossed with another such individual). The expected offspring genotype ratios are YY : 2XY : XX, or three hermaphrodites (YY and XY individuals) to one female, setting the stage for the establishment of a gynodioecious population. Current Biology 2018 28, R80-R83DOI: (10.1016/j.cub.2017.11.052) Copyright © 2017 Elsevier Ltd Terms and Conditions