- 1). Write down the genotypes of each parent. Assign letters to each gene and capitalize the traits that are dominant. For example, two parents' genotypes for hair color (A/a) and eye color (B/b) might be AaBb and aaBb.
- 2). Create a 4x4 table to record the possible offspring genotypes. If you have already created a 2x2 table for a single-trait Punnett Square, then simply expand upon the existing table.
- 3). Write in the first set of genes from Parent 1 (the A's) above the top row. You will scribble down each gene twice. Using the example in Step 1, you would write: A, a, A, a.
- 4). Complete the top row by supplying the second set of genes from Parent 2 (the B's) in such a way that you represent every combination the four genes could create. For Step 1's example, the top row would read: AB, ab, Ab, aB.
- 5). Repeat this process along the left side of your grid using the reverse traits. List the first set of traits for Parent 2 (the As) and the second set of traits for Parent 1 (the Bs). Following the given example, the left side would read: aB, ab, ab, aB.
- 6). Combine the top and left lists inside the table in the box that intersect each row and column. For example, the first box should combine AB and aB to get AaBB. What this means is that if this scenario were to occur, then the offspring would contain a dominant and recessive gene for hair color and two dominant traits for eye color. The phenotype, or visible end result, of this combination would be dominant hair and eye color (which in humans is brown). Continue this process with all 16 boxes to learn each of the possible scenarios.
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