Punnett Square Calculator | Punnett Square Generator

Punnett Square Calculator

Number of traits in cross: 2

Edit Alleles:
Parent 1:
Trait 1
Trait 2
Trait 3
Trait 4
Trait 5
Parent 2:
Trait 1
Trait 2
Trait 3
Trait 4
Trait 5
Dominant Alleles:
Trait 1: N/A     X   x   
Trait 2: N/A     Y   y   
XxYy × XxYy

The Punnett Square, named after the British geneticist Reginald C. Punnett, is a tool that allows us, based on the genetic information of two parental organisms, to predict the genotypes and phenotypes of their offspring. With the help of the Punnett Square Generator that we present here, you will be able to take advantage of this wonderful genetic analysis tool.

To use the online Punnett Square Generator you must follow these steps:

  1. Choose the number of traits you are going to consider for each parent organism.
  2. Indicate if you want to carry out the prediction of genotypes or phenotypes.
  3. Define the letters with which you will designate the alleles of each trait. By default, for alleles of trait 1 the letters Aa are assigned, for alleles of trait 2 the letters Bb will be assigned, for trait 3 the letters Cc will be used and for trait 4 the letters Dd.
  4. You then have the option to indicate which of the alleles will be dominant.
  5. Once the above is done, to generate the punnett square you only need to press the “Generate Punnett Square” button. When you press this button, the punnett square will be displayed automatically. At the same time, you can see in list format the repetition frequency of each combination of alleles, for this you will only have to press the “Show Frequencies” button.

After explaining how to use the punnet square calculator, below we present the basic theoretical concepts related to the Punnett Square, so that you have all the necessary elements to understand in depth the great potential that this wonderful genetic prediction tool offers us.

What is a phenotype?

The set of observable characteristics of an individual, taking into account its morphology, physiology and behavior, is called the phenotype. An individual’s phenotype not only refers to observable characteristics, but also groups molecules and structures such as RNA and proteins produced as encoded by genes; which is called the “molecular phenotype”.

What is a genotype?

Before giving the definition of genotype, we must know what a gene is. A gene is a piece of DNA that contains the information necessary to determine a trait. Put more simply, a gene determines a trait. For each gene located on a chromosome there will be another located on the homologous chromosome, in the same place, which will carry information for the same character: These genes are called alleles. The information that the allele genes have can be the same or it can be different.
Knowing what genes are, we will now explain the concept of genotype. The genotype concept refers to the set of genes that, when expressed, determine the characteristic or trait of the individual. In other words, a genotype is a classification of the type of variant present at a given location (ie locus) in the genome.

Punnett Square definition

The Punnett Square is a grid-like diagram used to predict the outcome of a particular cross or breeding experiment.

This tool helps display all possible gamete allelic combinations in a cross of parents with known genotypes to predict the probability that their offspring will possess certain sets of alleles.

In the Punnett square, uppercase letters are used to represent dominant alleles and lowercase letters to represent recessive alleles. Thanks to this, it is very easy to observe how the alleles are inherited or transmitted to the offspring of the parents.

How to do Punnett Squares

To make Punnett squares you must follow these steps:

    • Step 1: Identify the genotypes of the parent organisms. If you are currently studying genetics, you will notice that on many occasions the statements of the exercises already specify which are the genotypes of each parent. For example, if the statement of the exercise says something like “The crossing of two parents with the following genotype: Aa and aa”, you would already have the genotypes clearly identified. On other occasions it is necessary to know how to interpret the information provided in the statement, as for example in the following statement: «The crossing of a short pea plant with one that is heterozygous for height». To identify the genotypes we must know that heterozygous always means one of each letter, so we would use “Aa” (where “A” = tall and “a” = short). The only way for a pea plant to be short is when it has two lowercase “a”, so the short-statured parent is “aa.” Thus having the intersection Aa x aa. Another example of genotype identification will be done by taking chickens as study subjects. Brown is dominant (B) and white is recessive (b). Let us try to identify the genotypes from the following statement: “Predict the offspring from a cross of a white chicken and a brown chicken if the mother of the brown chicken was white.” The only way for the white chicken to be white (the recessive trait) is if its genotype is homozygous recessive (2 small letters), so the white chicken is “bb”. Now, the brown chicken’s genotype could be “BB” or “Bb.” If his mom was white (bb), then this brown hamster must have inherited a little “b” from his mom. So the brown in our cross is “Bb” (not “BB”), and our chicken cross is: Bb x bb.


    • Step 2: Write the formula for the match you want to evaluate with the Punnett square. The formula for the chicken cross presented above is Bb x bb.


  • Step 3: Draw a grid. Then divide the letters of the genotype for each parent and place them on the left side for one parent and on the top side for the other parent, as shown in the image below:
How to do Punnett Squares - A
  • Step 4: Determine the possible genotypes of the offspring. To do this we will fill the grid with all possible combinations. You can assign a color to each of the combinations to make it easier to identify the frequency of occurrence of each combination. The following figure shows an example of this:
How to do Punnett Squares - B
  • Step 5: Interpret the results obtained. In the case of our example we have that if we carry out an analysis of the phenotypes we would have that 50% of the chickens descending from this crossing would be brown and the other 50% would be white. But if we carry out the analysis based on the genotypes, we would say that 50% of the descendants will present the Aa genotype and the other 50% will present the aa genotype.

We recommend you practice with the punnett square calculator so that you fully understand the steps explained above.

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