The Full Red Debate Resolved?

F2 Full Red male X VEG female

On the face of it there is nothing remarkable about the guppy you see above. It looks like a young wild-type or Vienna Emerald Green (VEG) sword.

In fact it is totally amazing. For reasons other than its aesthetic appeal.

This is the grandson of a Full Red guppy male outcrossed to a VEG female.

So why am I shouting?

Just think about it. In the second generation of the cross this male has lost all the full body red of his grandfather. For perspective, here is a sibling from the same cross.

Sibling. Note the greenish iridescence at the base of the peduncle.

You might still be wondering what the fuss is all about. Well, there has been two theories kicking about in the guppy community about the Full Red. Recently I was told by a correspondent that he had it "on authority from an American guppy judge" that the full red was a type of Moscow. The theory is that the full body red color is due to the Moscow gene which normally creates full blue, green or full red guppies.

The Moscow gene (or genes!) is highly Y-linked. What this means is that it is only passed on from father to son because it is located on the Y chromosome and the Y chromosome is only found in males. It has a sex determining region (SDR) that determines the sex of the fry. Genes physically located near the SDR never cross over to the X chromosome. So a female, which has two X chromosomes (the male has one) cannot ever be in possession of a gene in close promixity to the SDR. A female Moscow can never be genetically a Moscow. And she cannot pass on the Y-linked color traits to her sons because she does not have a Y chromosome.

So here's the rub. The wild-type male descended from the Full Red male does not express Moscow attributes. None. Zilch. It is not a Moscow. It must be the case that you can have a Moscow that is entirely red, but it is not the case that all Full Red males are also Moscows. That is the advantage of doing basic guppy genetics research with genetics tools. You get to decide these kinds of questions for yourself without the need to appeal to authority.

There is another observation to make, given the inheritance characteristics of the X and Y chromosomes. The F1 VEG male apparently does not carry Y-linked red genes, other than the red spots which are standard issue on all guppy males, wild or domestic. (Because there are red spots, this dismisses the argument there is a red pigment mutation suppressing red color in the VEG type male.) Either that or the expression of those genes are suppressed by some other gene. This raises the possibility that the full red color in this Chiasson Full Red strain is either X-linked or autosomal. Since X-linked color crosses over to the Y chromosome, and presumably selective breeders would have selected for both X and Y-linked red color, it is likely the full red color in this strain is due to an autosomal gene.

Additional evidence for the view that the Full Red gene(s) is either X-linked or autosomal comes from another cross I performed with the Chiasson Full Reds. I was able to produce full red Moscows, which means the full red gene or genes could not be Y-linked. Plus you have all the evidence of the Red Moscows. You cannot create Red Moscows from Y-linked genes because only male Moscows can be used in outcrosses.

There is another theory, which is championed by another influential guppy judge. The judge claims that the Full Red guppy color is due to at least six different genes. This particular judge eschews genetics so I am sure he is unaware that such a statement isolated from its context is prima facie true. In fact all colors are multigenic. That is because color cells and their color organelles, the chemical steps in the manufacture of color pigments, gene regulation during development and the multiple interactions of color cells through cellular signaling all involve the products of many different genes. But the judge's statement stands in contrast to the view that a single gene causes the wholesale change to red of all the color cells in the body of the guppy.

An example of a gene that can cause a wholesale change in color in the guppy is the albino gene. It causes a complete lack of black color in the guppy. Is there a red mutation that causes all color cells to develop as red? My cross seems to support this theory. In the Color Manual book I am writing I examine this case in much more detail and show that the truth actually lies between the two contrasting views.

One of the results of my cross that has me leaning heavily in the direction of a single gene is the fact I got three basic phenotypes. One was  no full red (6 or 8), another was full red (6 or 8) and the other was an intermediate form, shown here (20 or 30).

F2 Intermediate Phenotype. In fact the F1 males looked like this, suggesting there is a recessive gene involved. Is it the Full Red gene?

If there were six different genes, you would expect there to be a bigger range of phenotypes. The odds of a single male with all six genes in the second generation of the cross are very low. And yet look at the full red phenotype. Solid red. Check out Oscar's Moscow X Full Red documented in the guest blog on this site. You will see the same phenomenon. Within a couple of generations he produced a Full Red Moscow. The argument can be made that all the red genes are on a single chromosome and are inherited as a unit. That is a possibility. I'll have to think about that...

There is much more to this cross than I have mentioned here, but I think I have given you enough to ponder about. I would love to hear your comments, either in support or in contradiction to what I have written here.

I will leave you with these teasers. It is possible that the VEG female brought a gene or genes into the cross that actually suppressed the expression of "full red" color in the male. The fact that some males were full red, some males were not, and some males showed a mixed phenotype suggests a recessive gene is at work here. Is it the full red gene? Is it autosomal?

The wild-type male looks remarkably like a VEG male, right down to the greenish iridescence at the base of caudal. Does the EGI gene actively suppress full body color? Since the full red sibling appears also to be expressing the EGI gene (he has green iridescence at the base of his peduncle), this theory is doubtful. (I actually think he is expressing the Mg gene from other crosses I have conducted with this strain.) But the three basic phenotypes suggests there is indeed a recessive gene at work here. What is it?

The second puzzler is the expression of swords in the VEG F1 male. Normally it is thought that the sword gene is recessive relative to the triangle or delta shaped fin. Why is it expressed in the F2 VEG male who presumably has the same Y-linked delta tail genes as his Full Red sibling? Why does the Full Red phenotype not express the swords? I have a theory about that, but I'll let you kick it about in your head. Ain't genetics fun!

BTW I am not going to be attending GuppyCon because I got called up for jury duty. But I have sent Bill a video to take my place.