A Punnett square is a tool that can help to understand how certain traits are passed on from parents to offspring. It is named after Reginald Punnett, an English geneticist. In this article you will learn use the Punnett square to do a monohybrid cross; that is, to figure out how ONE trait is passed on from parents to offspring.
Instructions
Drawing a Punnett Square
1. Determine what trait you would like to use for your example, such as B = brown eyes; b = blue eyes. Remember that a gene has two alleles (e.g., BB, Bb, or bb).
2. With your pen or pencil, draw a medium-sized square and a cross inside it on your piece of paper so you have four small boxes next to each other.
3. Write the gene(s) of one parent across the top of the Punnett square and the gene(s) of the other parent along the left side of it.
4. Fill in the Punnett square by writing the letter above and beside each box in each individual box. (The capital letter goes first followed by the lowercase letter.)
5. List the combination of genes you got as a result to figure out the probability of the offspring inheriting that particular trait. Let's use BB and bb as an example, with one parent having brown eyes and the other having blue eyes. The combination we get by using the Punnett square is BB, Bb, Bb and bb. This means there is a 25% probability the offspring will be homozygous with brown eyes, a 50% probability of heterozygous with brown eyes and a 25% probability of homozygous with blue eyes.
Tags: brown eyes, blue eyes, Punnett square, brown eyes probability, eyes probability, from parents