Re: Cost of sex - a bargain!


"allanm" <allangmiller@xxxxxxxxxxxxxx> wrote in message news:1155496649.831146.295900@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

<snip>

Let me recast this for the dogmatically entrenched. Think of it as a
simple exercise to make me look stupid(er).

I am a selfish gene. I am capable of making a female go down the route
of producing multiple copies of herself without the aid of a male. - to
pull the stunt of asexual defection and reap that juicy Cost of Sex.

If I do this, she will get to produce multiple copies of herself,
instead of half-copies. (Not sure how it will really benefit HER), but
there you go. My other-allele pals will gain because they will get to
produce more copies of themselves per offspring. Not sure how either
fact benefits ME but there you go.

How do I accomplish the trick?

I think you are confusing yourself with this talk of gene motivations.
It is really very simple, even if you look at it at the gene level.

Consider a species that lives in a cold, dry environment. It is
completely sexual in that environment. Females pay the bulk of
the costs of reproduction. The species is diploid and has a
reproductive system much like mammals

On an autosomal chromosome in this species is a locus which is involved
in the meiotic process. There are two variant alleles, A and a.
Both alleles are common in the population. In the normal cold, dry
environment in which the species currently lives, it doesn't make
any difference whether you have A or a alleles. You are sexual in
either case. But in some other environments, it matters. If you
are female in a warm environment, and you have even one copy of the
a allele, meiosis is suppressed. That is, a germ cell will develop
into a diploid egg that does not require fertilization. Similarly,
if you are female in a wet environment and you have two copies of
the a allele, you will reproduce asexually.

Ok, our species has been reproducing sexually in its cold, dry
environment for some time. But now the environment changes. The
question is whether the a alleles will increase in frequency. I
claim they will. You apparently claim they will not.

First, let us look at what happens if the environment becomes warm.
Now all of the AA females remain sexual, but the Aa and aa females
become asexual. For now, say that males remain sexual in any case,
and don't care about that locus. All of the offspring of aa females
will be aa. All of the offspring of Aa individuals will be Aa.
But the offspring of AA females will be mixed, since they will
sometimes mate with Aa or aa males.

So we can say that the frequency of A alleles must fall and the
frequency of a alleles must increase. It is tempting to say
that this continues only as long as the male population has a
alleles. That is, once the male population becomes purely AA,
and the sexual female population becomes purely AA, then the
attrition of the sexual population stops. But this fails to
take into account that the asexual females are producing twice
as many _female_ offspring as the sexual females. Unless the
sexual females are _much_ more fit than the asexuals, the sexual
females are headed for extinction. The A allele, though, may
survive.

Ok, now lets look at what happens if the environment becomes
cold and wet. Now a female needs to be aa to be asexual. And,
as above, the asexuals breed true and produce twice as many
female offspring as the sexuals. In this case, it it clear that
once again, sexuality is headed for extinction. And this time,
the A allele is extinguished as well.

So what, if anything, is wrong with this analysis? I'm pretty
sure you look stupid, but the real question is "Do you _feel_
stupid?"

.

Relevant Pages

  • Re: Cost of sex - a bargain!
    ... Consider a species that lives in a cold, dry environment. ... Both alleles are common in the population. ... Now all of the AA females remain sexual, but the Aa and aa females ... female offspring as the sexuals. ...
    (talk.origins)
  • Re: Cost of sex - a bargain!
    ... Both alleles are common in the population. ... Now all of the AA females remain sexual, but the Aa and aa females ... female offspring as the sexuals. ... Because I did not say that asexuality would always be ...
    (talk.origins)
  • Re: Cost of sex - a bargain!
    ... of producing multiple copies of herself without the aid of a male. ... Now all of the AA females remain sexual, but the Aa and aa females ... female offspring as the sexuals. ... Because I did not say that asexuality would always be ...
    (talk.origins)
  • Re: Origin of sex - not why but who and when?
    ... to keep flipping between individual fitness and cost, ... and a 2:1 copying bonanza for every gene. ... This swamps the sexuals, but also demands ... I think females *are*, in a sense, 'programmed' to produce at least two ...
    (talk.origins)
  • Re: Harvards president apologizes
    ... >>Are you suggesting that females play no role in spreading alleles ... while many or most males have been eliminated from the gene ... that the results of sexual selection forces acting on all vertebrates ...
    (sci.geo.geology)