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Gene Mixing

*Hemidactylus* hemidactylus at my-deja.com
Tue Aug 3 13:04:16 EST 1999

In article <7nvcsd$rev at dfw-ixnews11.ix.netcom.com>,
  "BlaDe" <icontrol at ix.netcom.com> wrote:
> Why cant you mix a dogs eggs and a cats sperm to get a wierd type of animal?

They are not only separate species, but they belong to different carnivore
families. Cats are felids and dogs are canids. I don't know the exact number,
but there is a large expanse of time separating the dogs and cats.

Interbreeding is an issue central to evolutionary concepts of species. A so
called "good species" is something which is reproductively isolated from
closely related populations. This concept does have its rough edges. There
are instances of hybridization between groups that are considered members of
separate species, but in general, this a handy rule.

A related issue here is reproductive isolating mechanisms (RIM's). There are
several types of isolating mechanisms which serve as a block against breeding
between two individuals from different populations. The isolation might be
behavioral, seasonal, or even genetic. With strong enough isolation comes

Two individuals might have genetic incompatibilities ranging from having
different numbers of chromosomes, having genes (from mother and father) which
do not function together well, or having an incomplete set of genes for
important developmental steps. There are other considerations. My treatment
is painfully inadequate.

You might find answers to evolutionary level questions in evolutionary
biology texts by either Futuyma or Minkoff.

> Same things with humans.  Does the sperm die immediatley when hitting the
> egg?  Something must be happening.

You might find answers to these questions in developmental biology texts (eg
Scott Gilbert's _Developmental Biology_). There is lots of work being done on
both sea urchin and mouse fertilization. The details are fairly complex.
There could be species specificity "checkpoints" along the way from egg and
sperm being attracted all the way through fertilization. This helps ensure
that there isn't wasteful development of inviable hybrid embryos. These
mechanisms aren't perfect though, I'd imagine.

The mechanisms that pertain to a neuro perspective would probably be the
prezygotic behavioral types or seasonal types as they sometimes could tie
into biological rhythms and such. If two popuations breed at different times
of the year, there isn't much chance of genes flowing back and forth. Drift
and selection can operate in this context (drift especially if the population
is very small).

Scott Chase

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