How to work with Punnett Squares
Used in selective breeding, Punnett squares are used to predict the outcome of a crossbreeding of two individuals by diagramming all of the possible combinations that may come out of the pairing. Originally limited to use by professional biologists in controlled experiments, this technique is now often used by hobbyists breeding animals; a notable example is the ever-present pet store betta fish. With visual traits linked to specific markers, it is possible for breeders to predict a specific appearance.
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Things You'll Need
- Paper
- Pencil or pen
- Information on traits and genetic markers for your parental subjects
Instructions
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1
Grab your pen and paper and write the gene alleles possible from one parent, ordering them vertically down the side. Use capital letters to indicate dominant alleles and lowercase letters for recessive alleles.
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2
Repeat the first step for the second parent, except order the pairs across the top horizontally.
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3
Make gridlines and fill them in with the potential combinations, matching the vertical option and the horizontal option at each intersection.
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From here you can see every possible combination of the offspring from the two parents and figure the probability of offspring having any of the different combinations of the alleles.
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These instructions are for the simplest sort of Punnett square and can be scaled to account for different independent genes.
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Tips & Warnings
Punnett squares are not applicable to all allele pairs because of complicating factors such as having alleles that are physically linked to chromosomes. This to a large degree is why gathering information on the genes you want to check is imperative.
