Julius B. Lucks/Meetings and Notes/SMBE2007/nei lecture

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Deborah Charlesworth (Edinburgh): The evolution of sex chromosomes - similarities and differences between plants and animals

Tue Jun 26 06:58:50 EDT 2007

Words to Look Up

  • dioecy
    • dioecious
  • PAML


Dr Nei's work on evol of sex chromosomes

  • how scelection can act on a modifier that reduces recomb, including modifiers on sex chrom themselves
  • why recomb lost? - sex chromosomes don't recombine
    • if sex determined by 2 or more genes - must inheret them together
  • how is recomb lost?
  • what are consequences of loss of recomb?
    • Y gene poor - Y and X homologs and Y has lost
    • is genetic degeneration caused by fact that Y heterozygous?
  • 'Theory shows that sex chromosomes should evolve low recombination'

Why Plant sex chromosomes?

  • test the theory
  • in plants can study how separate sexes evolved
  • plant sex chrom evol young
  • evol indep many times over
    • tell which features found when sex chrom evolve
    • maybe more than 100 times
    • Darwin noticed
  • degeneration processes not affected by prior existence of sex chromosomes
  • Darwin noticed - male and female flowers can look very similar - evolved recently and haven't lost redundancy
  • Human Y about 1/3 of X - recombine in very small portion of autosomal region that are homologous
  • Silene dioica - 230 Mb Y
  • Papaya - most sex chrom pseudo-autosomal, and only small portion of Y is male-specific
    • very young sex chromosome

Why Recomb Lost?

  • requires several genes
    • at least 2 - male and female suppressor genes - one on each chrom (so that don't end up with both and be neuter)
  • argument for 2 or more evol steps
  • sex determining loci must be initially be linked for separate sexes to evolve
  • higher allocation to male function will generally lower female functions
    • holly - male (many flowers, female few)
    • something about huge pumpkins