Re: [pyrnet] Recessives and carriers

["Linda Weisser" <lmweisser@olywa.net>]

----- Original Message -----
From: <JGentzel@aol.com>

<< It may be
ultimately safe to peresume every dog is from every litter, subsequent to a
carrier is also a carrier, but it is not correct. >>

You are probably right here but the presumption of that possibility may
well save some breeder from the shock of her life.  I think that it may be
better to anticipate the worst and get the best than vice versa.

<<Probability tells us clearly
that from generation "0" with the carrier to generation 1 it will be 50/50,
carriers Vs clear.  Generation 2 will be 25/75 carriers to clear.
Generation
3  will be 12.5/87.5 carriers to clear. >>

Probability may tell you that but no genetic statistician will.  And
remember that everytime you breed a carrier to a clear and have an
apparently normal litter you have raised the number of carriers in the
population which is, in part, how we got to the pass we are at now.  In my
post about the test breeding I talked about Sire #1 who turned out to be an
obligate carrier.  BUT, not until his *12th* litter was that known.
Contemplate for a moment the number of carriers that this dog left behind!!
Fortunately for the breed, he belonged to someone who exercised pretty
serious control over what happened to his offspring (even when bred by
someone else) and almost nothing out of those 12 litters was bred.  And of
the very few that were bred, they all belong to people who are absolutely
clear about what is happening and what they are doing.  In actual fact,
most of the breeder/owners of those offspring have ceased to use them.

<< From what you are saying any dog
with El Amour Bruno Balibasque in their pedigree has a 50/50 chance of
producing Dwarfs. >>

Theoretically and statistically, yes, that is what I am saying.  Unless an
intervening test breeding (either deliberately or inadvertently) has shown
that that particular Bruno descendant is not a carrier.  The litter of
which I have been speaking in which we unearthed the carrier was the result
of a Bruno great grandson bred to a Bruno great grandaughter.  In this case
both of these Bruno descendants had a 50% chance of being a carrier but we
had no idea of that fact.  Had anyone actually known the truth, the
breeding would probably never have been done, or at the very least it would
not have resulted in so much shock and heartbreak.  Generation 3 in this
case was not 12.5/87.5, it was 100% but even thinking 50% might have
helped.  I suspect that this same kind of link is involved in a more recent
dwarf litter.  We need to understand and recognize that in some cases
dwarfs are resulting from breedings of animals that are 4,5 and 6
generations descended from an obligate carrier (i.e. an animal that we know
has produced dwarfs)  And if there have been dwarfs in the intervening
generations, nobody has found it necessary to share that information.

Of course we know that not all descendants of any given obligate carrier
are themselves carriers.  We see enough double Klumbo litters to know that
that is not true.  But until we have a way to test for carriers, we would
be "foolish" to presume that our individual descendant did not have a 50%
risk.

DISCLAIMER:  I have no *personal* knowledge of Bruno ever having produced a
dwarf.  Therefore I cannot truly call him an obligate carrier.  The
assumptions upon which Joe and I are working here come from a lot of
information and a lot of work with dwarf pedigrees.

<<but at 8 or 10 generations later you are talking only a very
small percentage wise.    >>

Oh no, and that is why we keep seeing breeders blindsided by dwarfs.  Every
dwarf carrier in the past has more than reproduced himself in terms of
numbers of carriers, even if we were to assume that the % of carriers is
diluted.  Do you know (I'm sure you do) how many Pyrs are descended from
Klumbo?  Even if we take only the ones he sired, the numbers are amazing.
And 50% of those are carriers.  The numbers of actual carriers in a
population will rise sharply when a carrier male is used extensively at
stud.  So, even if you could reduce the % of carriers, the numbers will
increase.

Linda