Humans have an almost innate desire to understand what makes their bodies tick. Genetics gives them a glimpse into the underlying DNA structures that make up the building blocks of the human body. It lets them explore the results of gene combinations that determine the physical appearance of plants, animals, and humans alike. Punnett squares allow a scientist to calculate all the possible combinations of genes that can appear in the offspring of two given parents and determine the probability of any of their children exhibiting a certain physical trait.Through interactive Punnett square activities, students discover that because of dominant and recessive gene pairs, the genetic code (or genotype) can differ from a person's actual physical appearance (or phenotype).
Puppets are an entertaining way to introduce the idea of dominant and recessive traits. Give students six paper cutouts of animals or human figures and ask them to label one "mom", one "dad" and four "child". Choose a trait such as brown hair or blond hair; or short or tall. Explain that each person receives two genes for each trait, one from mom and one from dad but that only one shows in the person or animal's physical appearance because it is dominant. The other is hidden because it is recessive but can still be passed onto that person's children. Assign a genotype to each parent puppet. For example, mom might have one gene for brown hair (B) and one for blond (b). (Capital letters represent dominant traits while lower case letters indicate recessive traits). Dad might have two brown hair (B) genes. If your genetic code is the same from both parents, you will display that trait whether dominant or recessive. But if a child receives a recessive gene such as blond hair from one parent and a dominant gene like brown hair from the other, the dominant gene will be the visible one. Assign the parent puppets a certain genotype for one trait and have students color the puppets to show the physical appearance of each according to their gene combination. Draw a four-square Punnett grid and list mom's traits on the top edge and dad's traits on the left edge. Demonstrate how to read the gene combination for each box from the column and row labels of the parent's traits. Write the trait combination for each possible offspring in the corresponding box. Label one "child" puppet each possible gene combination and color to match the phenotype or visible physical trait that will appear in that child. Tape the puppets to craft sticks and put on a puppet show explaining how heredity works for another class.
Family Genetic Survey
Delving into the genetics of their own families provides motivation for students to explore heredity and learn what they have in common with family members. Give students a list of common and easily observable heredity features such as eye and hair color, tongue rolling and detached, or attached earlobes. Ask them to take a survey of their own family (parents, siblings, grandparents, aunts, uncles, cousins) and record the physical traits of each. Have them complete a Punnett square on their parents or grandparents and compare how the theoretical probability of certain traits in offspring played out with real life offspring.
Act It Out
Get students out of their seats and moving to create a living representation of a Punnett square. Make placards to hang around the students necks that list different possible physical traits of humans, plants, or animals depending on what type of genetics you are studying. Make sure that each trait has a dominant-recessive counterpart amongst the group. Draw large Punnett square grids on the pavement in sidewalk chalk or mark them out with tape on the floor of a large indoor area. Call out the genotype of the parents for a particular trait and have students who have those traits arrange themselves around the sides of the box in the right combinations. Ask the other students to arrange themselves in the offspring boxes in pairs that represent the possible genotypes. Each pair must determine which of them represents the dominant gene or phenotype. If both genes match in a box, both remain standing. If the box contains a dominant and recessive gene, the person holding the recessive card must sit to illustrate that the dominant gene determines the phenotype or actual physical appearance.
Online science games give technologically-oriented students a chance to practice creating Punnett squares and solving genetics problems through interactive computer activities. McGraw-Hill Virtual Lab and Oracle Education Foundation are two of the many websites to offer Internet-based Punnett square games.
- University of Georgia: Genetics Puppets
- McGraw-Hill Higher Education: Punnett Squares
- California State University, Los Angeles; Punnett Squares; Elizabeth Anne Viau; 1999
- Exploring Nature Educational Resource; Genetics Activity - Create the Kids; Sheri Amsel; 2011
- Exploring Nature Educational Resource; Genetics for Kids Mini-lecture and Punnett's Square Activity; Sheri Amsel; 2011
- Exploring Nature Educational Resource; Predicting Genetics Traits - The Punnett Square; Sheri Amsel; 2011
- Comstock/Comstock/Getty Images