[extropy-chat] Hybrids

[Anders Sandberg]

David Lubkin said:
> No one responded to the question I posed a couple weeks ago, so I'll ask
> again. It was asked in a reply to a religious thread, so many people may
> have missed it.
>
>>How is it that a horse and a donkey -- different species, with different
>>numbers of chromosomes -- can produce offspring?  What are the limits of
>>cross-species mating, besides incompatible hardware, e.g., horse and
>>gerbil?  Given species x, y and gestational periods g(x) and g(y),
>>respectively, what will the gestational period of an x carrying an x/y
>>hybrid be?

A fast google:
http://gslc.genetics.utah.edu/units/basics/conservation/tools/chromoanalysis.cfm

"For the mule, having parents with different chromosome numbers isn't a
problem. During mitotic cell division, each of the chromosomes copies
itself and then distributes these two copies to the two daughter cells. In
contrast, when the mule is producing sperm or egg cells during meiosis,
each pair of chromosomes (one from Mom and one from Dad) need to pair up
with each other. Since the mule doesn't have an even number of homologous
pairs (his parents had different chromosome numbers), meiosis is disrupted
and viable sperm and eggs are not formed."

Seems there are plenty of possible hybrids:
http://members.aol.com/jshartwell/hybrid-mammals.html
That page also has plenty of useful info about when hybrids can occur near
the end.

In short, I guess you need fairly closely related species since the
control programs among the genes otherwise may have shifted meanings, and
the different chromosomes will be sending contradictory orders during
development.

At least in Bison-Buffalo gestation length become highly variable due to
hybrids:
http://www.beefalobeef.com/hybrids.htm

> Beyond being interesting in their own rights, the limits of genetic
> differences that will produce fertile offspring without technological
> assistance are an important consideration in forthcoming human genemods.
>
> Just as I want some people living off-Earth in an environment that can be
> viably self-sufficient with primitive technology, I would prefer that
> humans not fracture into reproductively incompatible successor species.

If you follow Greg Stock's idea with putting the modified genes on an
extra non-inheritable chromosome this won't be a problem. Even two heavily
modified parents will have "natural" children - if they want to upgrade
them, they have to do it at an IVF clinic.

Then again, why is it bad to become a bunch of species? If a society can
create genetic modifications to create such a situation, then it can also
be remedied. In a loss of technology scenario where such abilities are
lost, then the loss of ability is likely a far larger issue than
reproduction.

-- 
Anders Sandberg
http://www.nada.kth.se/~asa
http://www.aleph.se/andart/

The sum of human knowledge sounds nice. But I want more.