Using a Punnett Square

Biology - High School

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Table Of Contents: Using a Punnett Square

1. What Is a Punnett Square?
A Punnett square is a chart that shows the allele combinations from a genetic cross. It helps predict the probability of a parental trait showing up in the offspring.
2. Information for a Punnett Square
To make a Punnett square, you need to know the genetic information from each parent. Each parent has two alleles, symbolized with letters.
3. Drawing a Punnett Square
When you make a Punnett square, the first step is to draw a square and divide it into four boxes.
4. Parental Alleles on a Punnett Square
Then, write one parent's alleles above the two boxes on the top and the other parent's alleles along the left side.
5. Filling in a Punnett Square
Copy the parent's alleles into the boxes, moving across the rows. Then copy the other parent's alleles into the boxes moving down the columns.
6. Completed Punnett Square
Each box now has two alleles, one from each parent. These boxes represent the genetic combinations that can occur in the offspring.
7. Allele Combinations and the Punnett Square
In this cross, there are three possible allele combinations for the offspring.
8. Probability and the Punnett Square
The probability of these combinations showing up in the offspring can also be determined.