Re: RC: Re: Re: Amblin/Racking/what ever

[CMKSAGEHIL@aol.com]

In a message dated 6/22/00 11:45:50 AM Pacific Daylight Time, 
truman.prevatt@netsrq.com writes:

<< The passing of genetic information is a discrete process not  a 
continuum.>>

Yes and no.  It is a continuum in the sense that all of the genetic material 
other than a few mutations goes back in an unbroken line through thousands of 
years of ancestors.

<< That is a half Arab has half it's genes from an Arab. If he is bred to a 
non
 Arab then the Arab contribution is 1/4. Ten generations later with breeding 
to
 nonArabs, the Arab content is 1 in 1024 and twenty generations it would be 1 
in
 over a million. >>

Nothing wrong with your math, Truman--only your premises.  What you are 
saying is exactly why practical folks don't get hung up on "purity" when 
maybe there was one stray ancestor "back there" 15 generations.  However, the 
sort of influence we're talking about in founding breeds is not a single 
ancestor, but rather a major percentage of the ancestry.  Example--Justin 
Morgan's pedigree is roughly half Arabian--give or take a little.  This is 
not the case of a single outcross to Arabs, but rather the breeding together 
of MANY horses who have a significant amount of Arabian blood over a period 
of time, so the percentage is not dropping.  If you breed half-Arabs to each 
other repeatedly, you will get a bell-shaped curve of how many actual genes 
are there from the Arabian ancestors--a very few will have primarily Arab 
genes at one extreme, and a very few will have not very many at the other 
extreme, but the bulk of the offspring will have something in the middle--in 
other words, something approximating half of their genes coming from Arabs.  

I'll give you an example of a single ancestor in a purebred pedigree.  Let's 
talk about Mesaoud.  It is rare to find him less than 6 or 7 generations back 
in a modern pedigree, and often he is much more--in my own horses, he runs 
anywhere from 7 to 13 generations back.  If he only showed up once, his 
influence would be negligible.  However, his offspring were used in SO many 
different programs that it is almost impossible to find pedigrees (other than 
some straight Egyptian pedigrees) where he has little or no influence.  With 
the use of Naseem in Poland and Russia, Mesaoud breeding even has a big 
influence there.  In our CMK pedigrees, however, it is not unusual to find 
horses with 100 or more crosses to him.  I have one stallion here who is 
19.8% Mesaoud, and I don't have any that are less than about 12%!  

This is the case with the foundation of other breeds, too.  Those individuals 
back many generations do not appear only once, because their descendants were 
bred back to each other time and time again to set breed type.  A modern TB 
may have hundreds of crosses to the three "main" Arab founding sires, if you 
really go back and trace extended pedigrees (not to mention those other less 
famous ones).  Same is true of Morgans, Saddlebreds, etc.  Not only is there 
a certain amount of linebreeding in the recent pedigrees, but a great many of 
those horses back 5 or 6 generations are closely related to each other, too.

Studies of mtDNA have shown this to be the case, too.  Again, just looking at 
the Arabian breed itself--there are only some 15 sire lines IN EXISTENCE, and 
something over 100 dam lines.  However, a great many of those dam lines share 
mtDNA, proving that they are actually THE SAME dam line, but that we simply 
don't have the paper trail to trace them to their root sources.

Mathematically, there simply were not enough horses in existence for the 
ancestors 15 generations back (or whatever number you want to pick) to have 
all been unique individuals.  There is a great deal of interrelationship 
"back there."  Distant ancestors are most likely repeated thousands of times. 
 For scientific references on this subject, I'd suggest you contact Michael 
Bowling--he's done a lot with mtDNA and historical relationships...

Heidi