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