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      Permanent link:
      http://www.ias.ac.in/article/fulltext/jgen/093/01/0241-0277

    • Keywords

       

      dioecy-mediated species evolution; plant unisexuality; sex-chromosome evolution; sex-ratio variation; XY–WZ transition; Y-chromosome degeneration.

    • Abstract

       

      Dioecy (separate male and female individuals) ensures outcrossing and is more prevalent in animals than in plants. Although it is common in bryophytes and gymnosperms, only 5% of angiosperms are dioecious. In dioecious higher plants, flowers borne on male and female individuals are, respectively deficient in functional gynoecium and androecium. Dioecy is inherited via three sex chromosome systems: XX/XY, XX/X0 and WZ/ZZ, such that XX or WZ is female and XY, X0 or ZZ are males. The XX/XY system generates the rarer XX/X0 andWZ/ZZ systems. An autosome pair begets XY chromosomes. A recessive loss-of-androecium mutation (ana) creates X chromosome and a dominant gynoecium-suppressing (GYS) mutation creates Y chromosome. The ana/ANA and gys/GYS loci are in the sex-determining region (SDR) of the XY pair. Accumulation of inversions, deleterious mutations and repeat elements, especially transposons, in the SDR of Y suppresses recombination between X and Y in SDR, making Y labile and increasingly degenerate and heteromorphic from X. Continued recombination between X and Y in their pseudoautosomal region located at the ends of chromosomal arms allows survival of the degenerated Y and of the species. Dioecy is presumably a component of the evolutionary cycle for the origin of new species. Inbred hermaphrodite species assume dioecy. Later they suffer degenerate-Y-led population regression. Cross-hybridization between such extinguishing species and heterologous species, followed by genome duplication of segregants from hybrids, give rise to new species.

    • Author Affiliations

       

      Sushil Kumar1 2 Renu Kumari1 2 Vishakha Sharma1

      1. SKA Institution of Research, Education and Development (SKAIRED), 4/11 SarvPriya Vihar, New Delhi 110 016, India
      2. National Institute of Plant Genome Research, Aruna Asaf Ali Marg, New Delhi 110 067, India
    • Dates

       

© 2017 Indian Academy of Sciences, Bengaluru.