Figures (3)  Tables (1)

    • Figure 1. 

      Sex determination system by the 'two mutations' model[13]. (A) One of a pair of autosomes has obtained a mutation of a certain sex sterility gene, 'M' to 'm' is a recessive mutation, 'f' to 'SuF' is a dominant mutation. (B) The other one autosome acquires the mutation corresponding to another sex sterility gene, thus generating proto-X and proto-Y, the precursor of sex chromosome. (C) Sterile genes are linked and sex chromosomes are preliminarily formed and dioecious plants emerged. The shaded part of the Y chromosome in (C) represents the sex-linked region.

    • Figure 2. 

      The main evolutionary routes to dioecy. (A) The gynodioecy-dioecy routes. (B) The monoecy-dioecy routes. (C), (D) It has been highlighted that dioecy may frequently revert to hermaphroditism. (C) In the gynodioecy-dioecy routes, inconstant males may help reversions to hermaphroditism. (D), (E) In the monoecy-dioecy route, there may be cycles between monoecy and dioecy.

    • Figure 3. 

      Two transposition pathways (copy and paste) leading to the emergence of XY and ZW sex determination systems in Populus deltoides.

    • TaxonSpeciesSex determination systemSex-linked region or genesOrtholog gene or familyReference
      BryophyteMarchantia
      polymorpha      		XY14 male-specific genes—[27,30]
      GymnospermGinkgo bilobaZWGbMADS18, Gb_15883,
      Gb_15884, Gb_15885,
      Gb_15886, Gb_28587
      		MADS-box (GbMADS18),
      RR12 (Gb_15883),
      RR2 (Gb_15884),
      ELF6 (Gb_15885),
      		[30−33]
      AtBAT1 (Gb_15886),
      AGL8 (Gb_28587)
      AngiospermFragaria virginianaZWGMEW, RPP0WGDP-mannose 3,5- epimerase 2 (GMEW),
      60S acidic ribosomal
      protein P0 (RPP0W)
      		[5, 34]

      		Spinacia oleraceaXYLG4 (66.98−69.72 cM and
      75.48−92.96 cM)      		—[35,20]


      		Silene latifoliaXYSlAP3, SlSTM, SlCUCAP3 (SlAP3), STM (SlSTM), CUC1/CUC2
      (SlCUC)      		[36,37]

      		Phoenix dactyliferaXYCYP703, GPAT3—[38]

      		Actinidia chinensis
      A. deliciosa      		XYSyGl, FrByARR24(SyGl),
      FAS1(FrBy)      		[39,40]

      		Asparagus officinalisXYSOFF, aspTDF1DUF247 (SOFF),
      TDF1 (aspTDF1)      		[41,42]

      		Diospyros lotus,
      D. kaki      		XYMeGI, OGIHB40 (MeGI)[42,43]


      		Cucumis melon
      		—ACS7, ACS11,
      WIP1, CRC      		—[43−46]


      		C. sativus—ACS7, ACS11,
      WIP1, CRC      		—[43−46]

      		Carica papayaXYCpSVPL, CpSERK, CpCAF1AL—[41,47−49]
      Myrica rubraZW59 kb female- specific
      region on chromosome 8      		—[50]
      Cannabis sativaXYsex chromosomes—[51]
      Vitis viniferaXYVviINP1, VviYABBY3INP1 (VviINP1),[52]
      YAB1 (VviYABBY3)
      Populus deltoides,
      P. tremula, P. alba, P. trichocarpa, P. balsamifera,
      P. tomentosa      		XY, ZWFERR-R’, FERR,
      MmS, ARR17      		ARR17
      [22,53,54]
      Humulus lupulusXYGr09-M—[55]
      Salix purpurea,ZWRRRR9/ARR17
      S. triandra
      [55,56]

      Table 1. 

      Results of sex determination of representative plants.