Re: [PyrNet-L] SAS. threat to Pyrs??

[Kshoffman@aol.com]

ARIEGE@xtra.co.nz writes:

<<but outcrossing is a good way of also introducing problems
 you've never had before >>

JGentzel@aol.com responds:

<< Or hiding the ones there only to be seen generation later.  This problem 
we 
 are told will not go away once it is there.>>

The most current knowledge and understanding of genetics and heredity 
indicate that linebreeding likely conceals (for generations) just as many 
things from a breeder as outcrossing might disguise. With complex modes of 
inheritance, you may not *know* something is there even with linebreeding or 
inbreeding on a very small gene pool you are intimately familiar with, until 
it is too late.

This is why linebreeding may perhaps be faulted in a sense as regards SAS in 
Newfs. Neither Janice nor I said linebreeding *caused* SAS.  What she said 
was heavy linebreeding for generations 20+ years ago likely allowed this 
defect to get a foothold across the breed.  I agree with her, this is likely 
what happened.  Especially if you factor in probable founder effect and 
popular sire effect.

Inbreeding and linebreeding result in the accumulation of more and more like 
pairs of alleles over generations, along with the discarding of anything that 
happens to be situated on the same chromosomes as the traits one is selecting 
against.  These other alleles on the chromosome that are being inadvertently 
thrown out with the undesirable ones quite possibly are beneficial as a part 
of some process or pathway coding for "non-visible" health traits, i.e., 
defect suppressor alleles, and/or optimal alleles involved in systemic 
functions such as metabolic efficiency, immune system efficiency, 
reproductive efficiency.

We have to remember that most dog breeders are selecting primarily for 
visible traits, things they can *see* and easily gauge, whether those be 
health related, temperament related, or conformation related.  Linebreeding 
doesn't necessarily *show you* what is happening genetically "behind the 
scenes" with each generation as regards multifactorial traits that aren't 
necessarily visible *until* such time that your realize or notice you are 
starting to see an obvious impairment of function.  This is especially true 
of fitness and general health traits and major defects that are not of a 
simple autosomal dominant or recessive mode of inheritance.

It is now generally accepted as fact in the scientific community that the 
accumulation of perhaps hundreds or thousands of suboptimal alleles over a 
period of generations of linebreeding/inbreeding results in what is commonly 
referred to as inbreeding depression.  Individually, a single one of these 
suboptimal alleles may present no problem, but collectively, once a number of 
these are accumulated, they begin to have a much greater impact as a group.

In a linebreeding program, you can't *see* that you are accumulating these 
suboptimal alleles until you have so many of them that the effects begin to 
be expressed and it becomes more and more obvious. This doesn't happen over 
one or two or three generations, it happens over several generations, 
possibly even over several decades if we broaden the scope to include an 
entire breed, and not just a single bloodline.  No line is immune from this, 
although some lines may reach the threshold that results in obvious 
impairment of function more quickly than others -- IOW, some lines can 
"tolerate" higher levels of homozygosity than others with minimal to mild 
impairment of function and lower than average defect rates, but these lines 
are likely few and far between.

The same holds true for polygenic defects and/or incomplete/variable 
penetrance, either of which is possibly the case with SAS in Newfs. You may 
not *see* with linebreeding/inbreeding that you are slowly concentrating like 
pairs of alleles, accumulating more and more of the pieces of the equation 
that result in outward expression of the disease, until you've crossed the 
threshold.  In that sense, linebreeding/inbreeding can "hide" some things 
from you for many generations, and fool you into thinking your line is 
"clean" when in fact it is not, which you will eventually find out once that 
drop of water goes into the glass that causes it to spill over, and then you 
find you have a BIG problem.

<<Do you want to get to from someone who does not want to know it is there.>>

But it is not necessarily a matter of *not wanting to know* it's there.  It's 
a matter of it not being expressed outwardly, so you can't easily *see* the 
problem until you've hit that magic combination of X number of genes and 
alleles that result in expression of the defect in a severe enough form to 
notice that "something is up."  By then, in a linebreeding/inbreeding 
program, the combination(s) that result in obviously noticeable expression of 
the defect are likely already "fixed in a homozygous state" and the only way 
to correct this problem is to go to unrelated stock that doesn't carry all or 
part of the combination of alleles that collectively produce the defect to 
varying grades of impairment.

In this sense, *avoidance* of linebreeding/inbreeding serves to reduce the 
risk of doubling up on the same allelic combination(s) that produce the 
defect, thus reducing the frequency of affected animals produced. Of course, 
it goes without saying that knowing as much as possible about the health 
histories of all the dogs in the proposed pedigree are necessary to 
accomplish this task (avoidance of doubling up on like alleles and like 
combinations of alleles) with each successive generation.  It is an ongoing 
process because obviously some animals will be carrying some of the alleles 
that add to the equation that crosses the threshold.  The idea is NOT to 
cross the threshold, and the odds of achieving this goal are greatly enhanced 
when there is more genetic distance, and thus more variation of genetic 
material, between two mates.

<<The linebreeding did not cause the problem.  The closer breeding simply
told you it was there.  It may be convenient to blame linebreeding, but it 
simply did not cause the problems in spite of what people say and believe.>>

I don't think anyone is saying linebreeding/inbreeding *created* the problem, 
just that these methods can quickly exacerbate the problem, especially if it 
is polygenic or variable/incomplete penetrance.  Linebreeding and inbreeding 
are much more likely to quickly increase the frequency of a defect that has a 
complex mode of inheritance than outcrossing is.  Inbreeding and linebreeding 
(merely a "slower" form of inbreeding) work very nicely for exposing simple 
autosomal recessive traits that a breeder can then select against and 
effectively "purge" from their lines.  However, the more knowledge we get 
these days as a result of the technological advancements in genetics, 
molecular/cellular biology, and biochemistry, the more obvious it is that 
genetics is **much** more complicated and complex than what was believed at 
the time when the books on animal husbandry and dog breeding that most of us 
and our mentors learned from were written. (Whitney, Onstatt, Little, Willis, 
Robinson, Trotter, Serann ..... just to mention a few authors of the "classic 
methods" on my own bookshelf.)

*New* and *current* scientific and genetic knowledge indicates that quite 
probably a vast number of genetic conditions that afflict purebreds ARE NOT 
simple autosomal recessives, but are due to much more complex modes of 
inheritance; polygenic relationships involving numerous genes and their 
alleles interacting with each other in tandem.  Some modes of inheritance 
involve a major gene or genes with incomplete and/or variable penetrance.  
Some defects of a polygenic nature are the result of one or more major genes 
working in tandem with groups of minor polygenes that collectively work to 
express differing severities or grades of a condition from appearing to be 
nonaffected (even though some or most of the genes which result in expression 
of the condition are there) to mild impairment which may go unnoticed, to 
moderate impairment to severe impairment.  In a linebreeding program, with 
defects such as these, you may well have no clue the problem is there until 
the defect expresses itself in such as fashion as it can't be denied, and you 
find yourself sitting in a pretty deep hole.

Kelley Hoffman
kshoffman@aol.com