From: crs@beta.lanl.gov (Charlie Sorsby)
Newsgroups: rec.pets.dogs
Subject: Re: Hunting ability in Labradors
Date: 24 Aug 92 02:19:19 GMT
Organization: Los Alamos National Laboratory

In article <1992Aug19.164726.18409@cbnewsl.cb.att.com> willett@cbnewsl.cb.att.com (david.c.willett) writes:
=  
= I believe Cindy (and others who've made similar points) are contradicting
= themseleves here.  On the one hand they say:
= 
= 	...Genetics are too complex to bring out clone after clone...
= 
= so "birdy" parents will produce "non-birdy" offspring.  Then they say that
= the non-birdy offspring should be sterilized because they would "ruin the 
= breed" if allowed to reproduce.
= 
= Don't the same laws of probability and inheritance which allow birdy parents
= to produce non-birdy offspring allow non-birdy parents to produce birdy ones?

Well, yes and no...

First there is something in what you say but, as with all such
probabalistic stuff, it's a gamble.

But first lets look at the "no" part of yes and no.  Let's say that
X (for ease of reference) is a non-birdy pup from a litter of,
otherwise, very birdy pups.  Why is X nonbirdy?  She received
nonbirdy genes from her parents.  Does she have any birdy genes?
Here's where the complexity enters the discussion.  I don't know
with any certainty if "birdiness" is a dominant or a recessive
trait but in the hypothetical case that you and others bring up, we
can make a (more or less) educated guess.

Since we're talking about breeders who are making a conscious
effort to produce birdy pups, then we must assume that both parents
of X were birdy.  *If* both parents were birdy but produced a non-
birdy pup, then we must assume that birdiness is recessive rather
than dominant.  [Aside:  Birdiness, as many other desirable traits
is almost certainly polygenic so it isn't quite this simple but the
essence is here.]

*If* birdiness is recessive, then to be nonbirdy, X must have
received *both* sets of nonbirdy genes.  Thus, she/he has no set of
birdy genes to pass on.

Before all you geneticists out there begin screaming, I've already
acknowledged that this is an over-simplified example.  Now for some
more qualification.  *If* this were a simple recessive based on a
single gene pair, it would be all over.  You have a pup, X, with an
undersired recessive trait.  He/she can *never* pass on that trait.
In this (almost certainly false) monogenic situation, this pup
should *never* be bred [if you're interested in producing birdy
pups] because bred with a birdy one, the first generation pups will
have at *most* a single gene (half a gene pair) for birdiness.
Each will receive at *least* one gene for nonbirdiness.  Thus, you
will, first of all, produce a higher percentage of nonbirdy pups
than you would if you bred two birdy adults.  You will also be
passing on more nonbirdy genes than if you bred two birdy adults.

Now in the more likely (and more complex) polygenic case, one must
ask "How nonbirdy is X?"  So far as I've seen, the discussion so
far has simply said "nonbirdy" implying totally so.  But, since
birdiness is almost certainly polygenic, maybe this pup is only non
birdy when compared with its ultrabirdy syblings.  Now the decision
isn't so clear cut.  But, I would still be hesitant to breed the
pup when it grows up.  One prefers to choose breeding stock from
those specimens that exhibit desired traits to the greatest extent
and undesired to the least.

But, I promised a yes as well as a no...

One author--I'm sorry, I've forgotten who--has claimed this:  To
begin a breeding program with limited funds, buy the worst pup from
a great litter rather than the best from an inferior (or even
mediocre) litter.  Given the alternative stated, I think I agree
with him.  And, he goes on to say that you must cull mercilessly.
As you produce pups, save only the very best for breeding stock.
His point is that the worst pup from an excellent litter is more
likely to have, hidden, genes that are needed to produce excellent
progeny that is the best from an inferior litter--even if that
"best" pup is better than the poorer one from the outstanding
litter.

Well, this is already far too long.  I hope it contains some food
for thought anyway.


-- 
Best,

Charlie "Older than dirt" Sorsby				"I'm the NRA!"
	  crs@lanl.gov
Newsgroups: rec.pets.dogs