Where does it end?

[mosgood]

Originally posted by AKIron
I'm referring to the violation of social taboos or decline of morals in general.

I'm not so sure that Morality is declining....  it IS definatley changing.

[Mathman]

Originally posted by hawker238
Please cite a scientific source from which you drew this conclusion....

 

If you can, pick up a book on population genetics or take a course in it.  Pay particular attention to the section in dealing with gene drift in a small population.  What happens is that you will get an ever increasing number of homozygous genotypes.  This means that offspring are more likey to have two copies of a specific allele of a gene.  You will get an increased number of offspring that have two copies of a dominant allele and some that have two copies of the recessive allele.

I would recommend a google search for inbreeding depression, population bottleneck, and/or population genetics.  While it is difficult to perform a test of this on humans (all sorts of legal issues), it is done all the time with animals (and not necessarily for testing these ideas).

[hawker238]

What I don't understand is why two parents with the same genotypes would produce an inferior offspring.  I understand that it produces a lack of variety from a evolutionary standpoint, but what about getting two similar... can't think of the word... haploids maybe?  What about getting two similar haploids from the parents causes defects.

[gofaster]

Did someone say "paleolithic"?

[Toad]

Don't misunderstand.

Linebreeding, done carefully and correctly can have outstanding, superb results. George Bird Evans created a wonderful line of "Old Hemlock" setters using it. Wehle did the same with his "Elhew" line of pointers.

The key factor is that these guys knew EXACTLY where they wanted to go and ruthlessly culled dogs from the line that showed any undesirable traits.

The problem is those "unknown" faults that crop up, the "hidden, possibly negative recessive characteristics that may go along with this ancestor's genotype".

Allergeies, hemophelia, vision problems.. there's a host of potential problems.

However, if you can get to the "promised land" and breed the perfect specimen, you can then repeat it almost ad infinitum. As in the Old Hemlock and Elhew dogs. At least until people dilute your "perfect" line with an outcross.  

[hawker238]

Oh, so most of these defects are recessive genes that are cancelled by normal breeding?  Now I got it.

Wouldn't that negative trait be necessarily expressed in the phenotype of one partner or, if both have a dominant gene and a recessive gene, wouldn't that be a one quarter chance of phenotype expression in the offspring?

[AKIron]

Originally posted by Toad
However, if you can get to the "promised land" and breed the perfect specimen, you can then repeat it almost ad infinitum. As in the Old Hemlock and Elhew dogs. At least until people dilute your "perfect" line with an outcross.  

Seems I remember that about 60 some odd years someone did want to do that with humans.

[Toad]

Depends on what you want out of the breeding doesn't it?

And no, the "negative" trait isn't always expressed in the phenotype of one partner. For example, many Black Labs carry a Chocolate gene and unless you know their correct "color ancestry" back 4-5 generations, you'd have to DNA test to know that. Fortunately, breeders generally keep good records.


Black coat color in Labs is important to some folks while others prefer Chocolate. Chocolate coloring is recessive. At one time, Chocolate pups were almost routinely destroyed by Lab breeders. So is Chocolate good or bad?


This is an oversimplification of course. If you're intrigued by this:

A Detailed Examination of Coat Color Genetics

or the "short answer".. just click on the color pairs to the left and see what you get.  


Coat Color Inheritance In The Labrador Retriever




And remember, we're talking something simple and obvious here, coat color. Progressive retinal atrophy (PRA) is not so simple; they've just now started building a DNA database for that and the test is barely affordable ($250 each dog). But if enough folks do the test, and use the results, PRA could be greatly reduced in a breed if not almost eliminated.

Imagine the possibilities with allergies to various things. Whew!

[Toad]

Originally posted by AKIron
Seems I remember that about 60 some odd years someone did want to do that with humans.

Yeah, they were pretty ruthless in THEIR culling too.

Which is one of the BIG problems with linebreeding humans. What do you do with the three-headed non-functional mistakes?

[AKIron]

Originally posted by Toad
Yeah, they were pretty ruthless in THEIR culling too.

Which is one of the BIG problems with linebreeding humans. What do you do with the three-headed non-functional mistakes?

Send 'em somewhere they'll fit in, Canada?

[Mathman]

Originally posted by hawker238
What I don't understand is why two parents with the same genotypes would produce an inferior offspring.  I understand that it produces a lack of variety from a evolutionary standpoint, but what about getting two similar... can't think of the word... haploids maybe?  What about getting two similar haploids from the parents causes defects.

The parents may have the same genotype.  The problem is that they may be heterozygous (one each of the dominant and recessive).  When they crossbreed, they may produce an offspring that is homozygous for that gene.  Thus, you can get either the desirable or the undesirable.  This doesn't include x-linked genes such as hemophilia (where the mother is a carrier and any male offspring could be affected depending on which allele is "given" by the mother).