genecutl at mendel.berkeley.edu
Tue Mar 1 15:09:07 EST 1994
In article <2ktq1h$cej at news.u.washington.edu>, toby at u.washington.edu (Toby
> In article <1994Feb28.185850.18629 at emba.uvm.edu>,
> Brian Foley <brianf at med.uvm.edu> wrote:
> >Haploid organisms, even if only a small portion
> >of their life cycle is haploid, play by different rules.
> I can't think of a sexually reproducing organism that *doesn't*
> have a haploid life history stage upon which selection can act.
> I'm willing to hear about some exceptions, though :)
There's not much selection on sperm and eggs. True, if the sperm
can't swim they'll be selected against, but there isn't much
selection apart from that and what selection there is doesn't
have any effect on their diploid forms (us).
> So, how are organisms with primarily haploid life cycles
> playing by different rules than organisms with relatively
> brief haploid stages? It seems to me to be a difference
> of degree, not of kind.
Look at budding yeast as an example of an organism that can
happily grow as either a haploid or a diploid. Selection
operates on both forms in the same way. The only differnce
is, if the diploid sporulates to generate four haploids,
those new haploids will have different genotypes from their
parent cell. Haploids that come from haploids and diploids
that come from diploids are identical to their parents.
In this respect there is a difference. Is this what was
meant in the original post?
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