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Instead of starting out and jumping into tail color genetics like most, I decided to start with tail pattern genetics. Why? Two reasons. First of all, it seemed that tail pattern genetics could be understood and isolated quicker than tail color genetics, and secondly, I'm a little colorblind (a genetic disorder, I might add). You probably shouldn't trust anything I say if it has to do with colors!

I chose the Yellow Mosaic Guppy because it's features were very distinct, much like the Cobra's. There appeared to be two distinct tail patterns as shown below.


This one shows a fairly recognizable pattern of black lines and spots (Called "large spot" from here on out)


This one shows small black spots that didn't seem to form much of a pattern (called "small spot" from here on out).

The assumption I started with was that the gene for a large spot mosaic pattern was dominant and the gene for small spot mosaic pattern was recessive. For this discussion I'll use the letter "A" for the tail pattern gene.

Since I don't yet know the genetic makeup of any fish, but my assumption is that large spots are dominant, I used the following assumptions:

The male is either an AA or Aa.
The females are unknown and could be AA, Aa or aa.

Assuming the male is AA, then the offspring would be one of the following, depending on what the female happens to be:
If the female is AA then all offspring will be homozygous large spots (AAxAA = 100%AA).
If the female is Aa then all offspring will be large spots (AAxAa = 50%AA(homozygous large spots) and 50%Aa(heterozygous large spots)).
If the female is aa then all offspring will be heterozygous large spots (AAxaa = 100%Aa).

If the male is Aa, then the offspring would be one of the following, depending on what the female happens to be:
If the female is AA then all offspring will be large spots ((AaxAA = 50%AA(homozygous large spots) and 50%Aa(heterozygous large spots)).
If the female is Aa then the offspring will be mixed 75% large and 25% small spots (AaxAa = 25%AA(homozygous large spots), 50%Aa(heterozygous large spots) and 25%aa(homozygous spall spots)).
If the female is aa then the offspring will be mixed 50% large and 50% small spots (Aaxaa = 50%Aa(heterozygous large spots) and 50%aa(homozygous small spots)).

If my main assumption is wrong and large spots are recessive (we now call large spots "a" and small spots "A") then I know I have an "aa" male. In that case the possible offspring would depend solely on the female as follows:
If the female is AA (homozygous small spots) then all the offspring will be heterozygous small spots (AAxaa = 100%Aa).
If the female is Aa (heterozygous small spots) then the offspring will be 50% small spots and 50% large spots (Aaxaa = 50%Aa(heterozygous small spots) and 50%aa(homozygous large spots)).
If the female is aa (homozygous large spots) then all the offspring will be homozygous large spots (aaxaa = 100%aa).


ROUND 1
Now that the possibilities and their outcomes have been laid down, it was time to do some breeding. I took a large spotted male and 4 females that came directly from Aquazone and mated them. of these matings I had two successful pregnancies.

Of the two successful pregnancies I raised 16 males. 12 males showed the large spot tail pattern and 4 showed the small spot tail pattern. From this alone we can eliminate many of the possibilities listed above.

ELIMINATIONS
Using my original assumption (large spot is dominant) the following can be eliminated:
*** All male AA options are eliminated as follows ***
Both male and female cannot be AA (large) since all offspring would have had to be AA (large).
The male AA (large) and female Aa (large) can be eliminated since all offspring would have to be large (either AA or Aa).
The male AA (large) and female aa (small) is also eliminated since all offspring had to be Aa (large).
*** One of the male Aa options is eliminated ***
The male Aa (large) and female AA (large) is eliminated since all offspring would have to be large (either AA or Aa).

Using the alternate assumption (small spot is dominant) the following can be eliminated:
The male aa (large) and female AA (small) can be eliminated since all offspring had to be Aa (small).
Both male and female cannot be aa (large) since all offspring would have had to be aa (large).

REMAINING POSSIBILITIES
There are two remaining possibilities under the assumption that large spot is dominant, and one remaining possibility under the assumption that small spot is dominant:

If large spot is dominant, the male from ROUND 1 has to be Aa and the female could have been either Aa or aa.

If small spot is dominant, the male from ROUND 1 has to be aa and the female has to be Aa.

From the 75/25% split we achieved, the most likely scenario so far is for a large spot dominant gene and the parents from ROUND 1 both having the Aa gene pattern. That is the only scenario that corresponds well with the observed patterns. The other remaining scenarios, however, cannot be discounted.


ROUND 2
From the offspring of ROUND 1, I mated a small spotted male with 3 of his sisters.

From the remaining three possibilities we can calculate some expectations:

For large spot dominance, the expectations of mating the aa (small spot) male are as follows:
A mating with an Aa female would produce offspring 50% large spot and 50% small spot (50%Aa and 50%aa).
A mating with an aa female would produce all small spot (100%aa).

For small spot dominance, the expectations of mating the Aa (small spot) male are as follows:
A mating with an Aa female would produce 75% small spot and 25% large spot (25%AA, 50%Aa and 25%aa).
A mating with an aa female would produce 50% small spot and 50% large spot (50%Aa and 50%aa).

The results of these matings are as follows:
  • Female 1: 5 small spots, 2 large spots.
  • Female 2: 2 small spots, 4 large spots.
  • Female 3: 4 small spots, 1 large spots.

This gives us a total of 18 males, 11 small spots and 7 large spots.

ELIMINATIONS
We can now eliminate aa (small spot) as a possibility for the females parents in ROUND 2 since they would have produced all small spot offspring (100%aa).
There is no help for the small spot dominance, as nothing can be eliminated.

WHAT WE KNOW NOW
If large spots are dominant, the parents in ROUND 2 were a male aa and a female Aa. Their offspring must be either Aa or aa.
If small spots are dominant, the parents in ROUND 2 were a male Aa and a female either Aa or aa. Their offspring could be AA, Aa or aa.


ROUND 3
This round attempts to nail things down. We can do this by mass mating the females born in ROUND 2 with a large spot male and observing the results.

If large spots are dominant, the female offspring of ROUND 2 must be Aa. By mating them with a large spot male (It will be either AA or Aa) we can expect to see AAxAa and AaxAa matings. The results from the former would be 100% large spots, and the latter would be 75% large spot and 25% small spot. The combined total would be 7 to 1 large (or 87.5% large spot and 12.5% small spot). Matings producing all aa (small spot) offspring are not possible.

If, on the other hand, small spots are dominant, the female offspring of ROUND 2 could be anything: AA, Aa or aa. From a mating with a large spot (aa) male, we can expect to see AAxaa, Aaxaa and aaxaa matings. The results would be 100% small spot, a 50/50 mix and 100% large spot respectively. Overall, this works out to be an average 50% large spot and 50% small spot offspring.

What does all this mean? It means that by observing the results of several matings we can get a very good idea of whether large or small spots are dominant.
If large spot is the dominant trait, the majority of offspring (87.5%) should have the large spot pattern.
If small spot is the dominant trait, the overall mix should be 50/50. There is also a 1 in 4 possibility of batches made up entirely of small spots (as mentioned above, this is not possible with large spot dominance).

15 females from ROUND 2 were mated to large spot males. 9 pregnancies resulted. From these 9 pregnancies there were 89 fry. Of those, 41 were male. When the males reached maturity they exibited the following characteristics:

  • Female 1: 5 large 0 small
  • Female 2: 4 large 1 small
  • Female 3: 2 large 1 small
  • Female 4: 4 large 2 small
  • Female 5: 2 large 2 small
  • Female 6: 2 large 2 small
  • Female 7: 6 large 0 small
  • Female 8: 5 large 0 small
  • Female 9: 2 large 2 small
  • TOTAL: 31 large 10 small

According to what we determined previously, if small spots were dominant we should have seen an average 50/50 mix and probably at least one all small spot batch of fry. This did not happen. The proportions of large to small spots tends to agree with the large spot being the dominant trait.

While still not absolutely conclusive, all the breedings performed during this experiment were consistent with the theory that the large spot mosaic pattern is the dominant feature. I will continue my efforts in nailing this down more tightly and if anything new comes up to alter this theory, I will post it here.

Greg Arihood

P.S. Since you've read down this far, here's a reward. The guppies below showed up during my final matings in round 3. There are 8 with these colorings. They are all pure Yellow Mosaic guppies, and quite striking if you ask me.


Click here for a larger view of the guppy tank


Please direct any comments, questions or criticisms to the Tail Pattern Message Board where they can be discussed by all.