Punnett Square Calculator | Punnett Square Generator (2024)

Table of Contents

• 1 Punnett Square Calculator
• 2 What is a phenotype?
• 3 What is a genotype?
• 4 Punnett Square definition
• 5 How to do Punnett Squares

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 hom*ologous 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.

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.

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 hom*ozygous 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: