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killifish and population genetics
Lets see if we can't kick of this week with a nice killi
Nothos show tremendous variety. If they didn't they
would become extinct. (Tree that does not bend breaks---
No doubt that in any population there are bad genes. For
the population of exist and ultimately evolve (not to
say into a new species but rather a better adpated form
of the same species) those bad genes have to be kept at
low levels. Natural selection will cull the population
to maintain this. To some extent mate selection also
does its part.
So... the more isolated the population the "stronger" we
must assume the populations collective genotype to be.
Which is why we rarely pick up genetic problems with our
nothos---all the bad genes are at very low frequencies.
While when we look at less isolated populations the
picture changes. Guppies and swords are good example.
Their environments are far less sellective as the fish
have widers distribution. Bad genes can escape selction
by moving to new environments were the selection critea
no longer exists. They may also find themselves in an
environemnt which selects in favour of a nearby gene (on
the same chromosomes). Such linked Bad genes genes are
difficult to get rid of as they afford the individual a
Now, we go fishing and we take a few fish from such an
environment. Lets sya we are lucking and we pull all
fish which lack that Bad gene. Great! But we can be just
as unlucky and pull out 1 fish with the trait (in spite
of the 1% frequency of that allele---the Bad gene for
our purposes). This 1 fish by some twist of fate lands
up in say Monty's fishroom where being the great breeder
he is spawns his fish in great numbers and distributes
them throughout the AKA. Initialy he started with 6 fish
of which 1/6 had the bad gene. By the time he is
finished the bad gene frequency has jumped from 1% to
17%. Worst of all it may be that Wright has bought a 2
pr of fish of whihc 1 pr has the Bad gene. Wright being
the die hard he is perservers with is fish to the point
were his fish have had it. In the mean time Monty has
picked up problems as by some chance the females he had
favoured the males with the Bad gene (becuase it was
linked to a gene which gave them better and more
attractive blue spangling---for arguements sake). As it
stands the frequency of the Bad gene is now 60% and
everyone is picking up problems now with fertility...
What is the moral of the story? Simply that genetics is
pot luck. We often can't see the genes that cause
problems. We tend to select for the visable traits which
for all we know is linked to some bad gene. Solution?
Gang breeding? What if the trait is linked to another
trait which promotes mate selection?
If we look back on the strains which have perservered we
find the good old AUS, GAR (mine dates back to 1981!),
whitei and a few nothos. Why were these so successful?
1) Large populations were set up and crossing out
2) High selcection critirea was practiced. Not just
colour and form but also in fercundaty.
3)some strains just had very little junk. Most nothos
and Cynolebias are resistant to ibreeding as they have
had to shed their bad genes long ago to survive.
With many of the imports now days maybe 10 prs comes out
of the wild. While the allele frequency of the bad genes
may be 0.1% this doesn't preclude bad genes coming out
with those 10 prs. With our new theories on maintaining
wild population we then set them up for group spawning
and before we know it (we have no test...) those bad
genes are everywhere. This is in complete contridiction
to how killies were bred in the hay day where a multiple
prs were set up and bred and from that strains were
Perhaps we are doing ourselves in with our breeding
practices? Your thoughts?
The names Monty and Wright were selected as we all know
them as damn-good-breeders and killikeepers so we can
keep this in perspective. Regardless how good a
killikeeper you are genetics is pot luck and inspite of
the best intentions, if you get bad stock that is all
you will ever have...
As a side not, the frequency of cystic fibrosis is
abnormally high in our current caucasian population. One
hypothesis for this is that it is linked to a gene or is
the gene which afforded some protection to the plague
which swept through Europe. This is just and example of
inadvertant selection of a bad trait while selecting for
Southern African Killifish Society Coastal & Offshore Coordinator
tyronegenade at yahoo_com
Please excuse my spelling.
I'm too lazy to use my spell checker.
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