Tropical Fish Keeping - Aquarium fish care and resources

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MOA 09-05-2009 08:27 PM

Breeding Fish, Spreadsheet and Punnett Squares

I made another spreadsheet, but this one isn't for stocking the aquarium. Instead, it is designed to help new fish breeders select and breed stocks. Below are links to a spreadsheet that calculates a dihybrid punnett square and the various genotypes and phenotypes that could arise.

Genotype: The genetic signature of an animal that will influence future generations

Phenotype: The appearance of an animal with regard to genetic traits (some animals will carry a trait but not show it and they will thus look as if they had the same traits as another animal).

Let's look at an example: let's say you want to combine a strain of fish with long tail fins with a strain that has red bodies. First you have to determine the genotype of the parental stock. The genotype describes the traits an animal carries and their dominance. For our purposes, let's say that the genotypes of our fish are as follows:

Father: Long Tail Recessive (the long tail doesn't normally occur in the wild type) with normal body color dominant (the fish comes from a long line of fish with normal body colors). This, in genetic alleles that the spreadsheet uses would be ttDD, where the tt represents a recessive tail structure and DD represents a dominant body type.

Mother: Normal Tail Dominant with red body color recessive. The genetic alleles for the spreadsheet would be TTdd, where TT represents a dominant tail structure and dd represents a recessive body color (red).

When plugged into the spreadsheet, the resulting offspring would have these traits:

As you can see, all of the offspring would not only look the same (phenotype 1), but also be genetically identical (genotype 24), and have the same alleles (TtDd). This means that the offspring will look like the wild type rather than either of the parents.

If the offspring were to be bred with each other, then their children would be quite diffrent (note that the alleles in the Father and Mother cells were changed to accommodate their new genes (type TtDd):

Since the offspring of the first generation carried the reccessive genes (both t and d) even though they did not look like they did, some of their offspring will begin to show those traits that did not show up at first. The new batch of offspring will mostly look like the wild type (9/16 or 56.25% will have phenotype 1). No less, some of the offspring will show long tails and red bodies. Of the offspring, 3/16 (or 18.75%) will have long tails (phenotype 3, genotype 22 or 25) and the same percentage will have red bodies (phenotype 2, genotype 26 or 27). Only 1/16 (6.25%) will show both long tails and red bodies (phenotype 4, genotype 28, ttdd).

Thus, only the second generation will show the traits that aquarist was looking for. If these fish that show both traits are bred from then on, then all of the offspring should show those traits as well:

Anyhow, play around with it and tell me what you think!


MonsiuerPercy1 09-05-2009 09:48 PM

Ah punnet squares. I remember doing these in Biology class. I have never incorporated it into breeding of fish but now I will have to contemplate...

MOA 09-05-2009 10:00 PM

Worldshaker 09-06-2009 12:45 AM

Oh man...i think i just fried my brain reading that. Too many big words for me that I dont know lol. I'll start with a basic question and let my brain absorb that for a few days...


Originally Posted by MOA (Post 238875)
First you have to determine the genotype of the parental stock

How would I go about doing that?

MOA 09-06-2009 09:23 AM


Determining the genotype of your parental stock requires you to know two things: 1) What traits are you looking for and 2) does that trait show up predominantly?

For example, let's say you are only concerned with breeding fish that have blue bellies and green backs. If one of the fish you want to breed only has a blue belly and blue is not seen in the wild type, then the first part of that fish's genotype would be tt. tt means that the trait is recessive and only shows up rarely. Since the fish has a normal-colored back, the second part of its genotype would be DD. DD means that the fish comes from a long line of fish that have the dominant (wild) form of some trait.

This help?


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