[continued from previous message]   
      
   generation, and the queen is able to do this in a way that maintains   
   high genetic variation among her offspring without having to share the   
   success with someone else.   
      
   >   
   >>> I had assumed that females result from fertilized eggs, each with a   
   >>> full, haploid M. structor genome and a haploid M. ibericus genome. Of   
   >>> course the problem with that is how you would get genetic divergence   
   >>> between the species, given recombination during meiosis.   
   >>   
   >> You might get recombination if the chromosomes match up, but after   
   >> repeated generations using the cloned male genome the species would   
   >> eventually become inbred M. structor, so there would be a species   
   >> switch eventually.  The first generation you get 50% M. structor DNA.   
   >> The next generation you become 75% M. structor DNA.  The next   
   >> generation you get 87.5% M. Structor offspring etc..  So when they   
   >> claimed that the genomes remained highly polymorphic and M. ibericus I   
   >> assumed that any hybrids had to be dead.   
   >>   
   >>>   
   >>>> It could be a case of Dawkin's selfish DNA.  The DNA of the queen   
   >>>> devised a means of perpetuating its genetics in a way that prevented   
   >>>> inbreeding depression, while being able to generate new segregating   
   >>>> genetic diversity among the daughter queens if the ants still have   
   >>>> genetic recombination before Meiosis I.   
   >>>   
   >>> How can you get or retain much diversity? Wouldn't that result in   
   >>> complete homozygosity after only a few generations? The male is   
   >>> contributing nothing.   
   >>>   
   >> If the nondisjuction event occurs in meiosis I, meiosis II results in   
   >> chromatid splitting in a full diploid genome.  I called this a   
   >> tetraploid egg because that is what the composition of the egg cell   
   >> would be if you started with a tetraploid and had a normal Meiosis I   
   >> separation of homologous chromosomes.   
   >>   
   >> Since recombination occurs before Meiosis I you maintain genetic   
   >> diversity and do not just produce clones.  When the chromatids split   
   >> at Meiosis II, recombined genetically unique chromosomes can go into   
   >> each egg cell.   
   >>   
   >> I used to make my genetic students understand Meiosis.  I would tell   
   >> them that if they understood meiosis that they would understand   
   >> Mendelian genetics.   
   >   
   > Nevertheless, you start with a single diploid individual, and that's   
   > limited genetic diversity. Recombination within a single genome can only   
   > introduce a little, and mutation a little. Keeping in mind that the   
   > effective population size (queens only) is likely to be small, how is   
   > any significant diversity maintained?   
   >   
   Mutation rate is essentially the same because both copies of the genome   
   of the 2N species is mutated every generation, and only half is   
   transferred to the next generation.  In this case the 2N is transferred   
   to the next generation, so it is the same as having another half mutated   
   genome incorporated instead.  The queen is highly heterozygous and is   
   segregating a lot of genetic variation, but this variation is not   
   segregating normally.  Instead of transferring half of the variation to   
   the next generation, she is transferring it all, but there are a near   
   infinite number variant packages that she can transfer when you consider   
   genetic recombination and new mutation.  Every meiosis she generates a   
   whole new set of chromosomal haplotypes to pass on to her offspring.   
      
   What is lost is the ability to gain new genetic variants due to normal   
   sexual reproduction.  In this case the queen posesses a highly   
   polymorphic genome that has been repeatedly tested and won out to create   
   an expanding population with the same starting genetics.  Each new queen   
   would have a different combination of genetic variation inherited from   
   the original queen.  Any combination that isn't as successful would be   
   out competed.   
      
   Ron Okimoto   
      
   --- SoupGate-Win32 v1.05   
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