The Development of an Inbred Line of Swine (Minn. No. 1) from a Crossbred Foundation1

"The wide segregation and general deterioration in performance generally believed to accompany the subsequent inbreeding of an F1 population did not occur."

http://jas.fass.org/content/2/2/129.short

Interesting summary found on this link. This is the kind of study we need to follow with DNA evidence. There appears to be both too few generations involved since the herd was closed and possible use of retained heterosis by strong selection for performance. The latter is gleaned from this quote; Rigorous selection for performance has been followed throughout the conduct of this experiment. Another possible clue is that the two breeds involved seem have been quite unrelated, which might result in fewer crossover points and fewer but bigger chunks of DNA to assort. These could remain heterozygous in the higher performing animals. The questions here are not unlike others posted, and may be an example of uniformity by heterozygosity.

Sounds about right, selecting for measurable performance would be selecting for the outliers on the lesser side of the IBC percent would it not; creating a slightly prolonged illusion of deifying natural law, enhanced because it is within a manmade time frame.

In the end I would think you will get Mother Nature’s attention no sooner or later then she deems necessary.

My question is, in a closed herd, in a natural environment such as the Yellowstone Bison where the animals were brought back from the brink of extinction, how much inbred regression has happened in that herd?

I don't have any insight into the question, but... a boar pig from this line was used here by my Dad and Uncle, ordered from J. C. Penney and shipped by train to the depot in town in a crate. I tiny bit of #1 influence would have remained in the crossbred herd that was continuous here until 1975, when they were all sold due to lack of a corn crop.

Good question Jack, I’m interested as well... I just hope the answer when G nome gets to it, will be layman enough for me to decipher

In my simple mind although I couldn’t narrow the range down with any accuracy number wise, herd size at closing and time would be only a couple of many factors.

So I bring it back to the mating system chart and consider that the 50/50 point would be 0 as to regression. The herd being closed contains us to the left side, 50% or better Homozgosity, if the starting population was half sibs or closer and some regression.

Over time nature will favour the less regressed with survival of the fittest maximizing her odds when confined to greater than 50% homozgosity levels.

I have right or wrongly considered her preferred balance to be 0 regression when not confined or center of the chart, and individuals ranging on either side.

My contention has been, with LL not so agreeable, that you reach a point in closed herds, that you must select for outliers in traits {growth-yw for example} merely to maintain the phenotypic AVERAGE of the herd...that selecting from the average and breeding to the average , while maintaining the genotype, would lower the phenotype due to regression resulting from the homozygousity of the middle...lots of assumptions on my part; wreck them all if you can

I'm just thinking out loud as usual

Stability of a phenotype would almost have to occur and be self regulate at a level that could accomplish a breeder’s often physical selection criteria and still perform to the breeder’s original specs.

Any breeding done in a regressed state beyond this level could not be subject to the original selection criteria because of that self regulating nature.

In the future technology may help us understand what we can’t see and more possibilities of refining the systematic restoration back into the visually tangible but more predictable purpose.

Because Mother Nature has no bills to pay, I have to consider that my requirements or specs are more than likely higher then hers and if wild populations in my mind basically find a neutral equilibrium of 50/50. I have to question whether a cow that can jump through all of my production hoops and beauty pageants is really as orderly as the IBC calculator says she ought to be.

I have a feeling my basic premise of the 50/50 Homo/Hetero of wild populations is off base though, lighting the rest of my rambling up in flames.

I assume the crossbred population was made because of imperfect adaptation in the two breedss of swine...That is to say they were missing something that mother nature or the herdsman required. So, we keep the new standard that neither breed could meet, and measure the population. Generally, I have noticed that this type of study is conducted on very distantly related populations within a species....Landrace and Tamsworth fit that description for me as I had Landrace for FFA projects in the past.

Assuming that it is a new standard, except for performance measured by, say litter number, litter weight at weaning, litter size at harvest, etc., then we see that each of these things is highly influenced by genetic distances between parents and generally exhibit true heterosis, some of it over both parents--not just high parent for any particular trait. How could we expect to see measureable reduction when we select for measures in the selected parents within the hybrid population that are extreme for phenotype?

My concern about breeding methods such as these is the same as for beef populations, in they lack true uniformity and predictability. They may have the opportunity of increasing weight each generation and to move the average forward.
This includes those on the females as well as males. While swine are not kept until growth has maxed out, beef cattle usually are. Can you imagine 1,000 pound sows to prouce the same 10 pigs a 250 pounder? Number of offspring 10 X 2.5 generations per year definitely skew the productivity curves for swine when compared to the 1 annual calf per cow beginning at 2 years, ending genrallly before 10.

The we reviewed with 1000 SNP markers seems to be appropriate. When two unrelated animals are mated, more loci are found in the heterozygous state in offspring. When two highly heteerozygous offspring are mated, the results are 1;2;1 for each segregating portion of DNA. In this example 1 Lndrace type homozygous: 2 hybrid types; 1 Tanmworth type. The combination of which genes are involved at each site possible varies from generation to generation, but then we select the ones most favorable for our measured trait. Heritability of that trait is measusred both against each parent type and against the F1, F2, BC1, BC2 types.

To differentiate a linebred population from the pool, the trait must be genetic and variable while phenotype is recognizeable. One should select for the smallest to see the genetic potential of the population for that trait or we are not looking at the full spectrulm. If we continue to select only the larger side of the bell curve, we will lmove the average and up we go. Sound familiar? Yes, those are elephant ads are again popular.