Genetics Discussion

[tjudy]

Hi All !

The discussion over on 'Wild or New' thread went off on a tangent, so I thought I would see where it goes.

Rich and I were talking about the role of inbreeding in the increasing incidence of undesirable traits. I made the point that inbreeding itself does not create defects, but that it can increase the incidence of 'defects', which I prefer to call 'undesirable traits'.

OK... here is where I thought it might be fun to go next... I am going to provide an example of the purposeful selection of a trait that would be considered undesirable, and then ask anyone who wants to participate to identify other examples like it.

The Black/gold gene in angelfish is, in one point of view, an undesirable gene to select for. (It is actually sturdier than the 'dark' gene, which was the first black color gene isolated in angels by Joanne Norton in 1971). This trait is coded for by a gene interaction known as complete dominance, BUT it has a nasty little twist. The gene for black (B) is dominant over the gene for gold (b). A bb fish is gold and very healthy. A Bb fish is black and very healthy. A BB male fish is black, not quite as healthy, but a very desirable fish to breed with. However, a BB female angel is sickly, and only rarely are they able to reproduce, and then the spawns are small and not very healthy.

8) The 'pot of gold' when I was breeding angels, back in the Dark Ages, was to identify a BB male using a test cross. If a BB male bred to a gold female produced all black fry... he was a BB male. The BB male to bb female produce 100% healthy black angels. A BB x Bb cross produced all black fry, but 1/4 of them (1/2 of the females) grew sickly and died (from not being able to compete). A Bb x Bb cross created the same problem, but to a lesser degree... and it also created gold angels which were... literally... a dollar a dozen (nobody but a breeder wanted a gold angel for some reason..). We wanted to avoid gold angels in spawns for another reason, which brings us to the point... gold angels are healthier than black angels, and if you try to raise them together the black get out-competed. We PURPOSEFULLY selected for a trait that had undesirable health issues! 8O

Joanne Norton worked most of this stuff out back in the 1970's. I am using it here as an example of a trait that we want, will often have some
strings' attached.

:?: Let's hear about other fish genes that we select for that have a slight problem associated with them.

 

[Richgrenfell]

Well,
Like i said in the other post, I never really bred selectivley but i do remember a thing with bettas. If you breed double tailed bettas with one another, there is a greatly increased incidence of spinal problems. The betta fiends that I know, always breed double tails to single tails. This is really the only thing i can recall on par with the thread.

Rich