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sex change in dinos



Sex change is quite common in animals.  I have published over a
hundred papers on various aspects of sex change in crustaceans.  In
verteb rates the XY mechanism of sex determi nation is confined to
mammals.  Other vertebrates have other methods.  Even birds have
a different mechanism, i n which the male is the homozygotic
form (having two identical sex chromosomes) while the female
is heterozygotic.

There is an old saying "A whistling woman and a crowing hen
                        are neither good for god nor men"
Have you ever thought what a crowing hen is?  It's a hen in the
process of changing sex to become a cock.  This used to be
not u ncommon in the days of free  range farm fowl, but in
modern factory produced chicks few birds ever live long enough
for this to h appen.  It's easy to produce artificially in the
lab.

In many reptiles  sex is not genetically controlled at all, but
under environmental control, usually the temperature of 
incubation during a particular phase of embryonic development
(usually quite a late stage, in fcat - long after co nception).
Crocodiles and turtles h ave been particularly well studied in
this regard.  This is h ardly sex change strictly speaking,
but is an example of how labile sex determination can be

Many coral reef fish change sex from female to male.  An example
is the blue-headed wrasse.  In this species  a male ty pically
assembles a harem of about a dozen smaller females.  If the
male is removed (eaten by a predator or removed by a scientist)
the largest female takes charge of the harem and changes into a
male, a process that takes about 2 weeks.

Many shrimps  do i t the other way round, from male to female.
Male sh rimps are generally smaller than female, and the
fecundity of females is cl sely related to h er size, since
the bigger she is th e more eggs she can carry.

I never did understand why Ch richton had to go to such lengths
to explain how he found it remarkable for dinos to change sex, and
had to introduce  amphibian DNA seemingly just for this plot
requirement.  I can think of no other reason form him to bring
this one up.  It would have made far more sense for his
"scientists" to have realized belatedly that sex is l abile in
other reptiles and so could be labile in dinos too.  
 
Did dinos change sex?  Perhaps, but how can we tell from the
fossils?  It would not surprise me at all if they did, and
the change could be either way round.

David

--
>From: David Brez Carlisle
bk090@Freenet Carleton.CA