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

 * 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