Updated October 2016
It’s easy to see why ears of genetic corn make ideal specimens for teaching Mendelian genetics. Experiments require minimal preparation. The ears can be reused (for years, with proper care and storage), making them relatively inexpensive. And there’s ample data available for analysis. Convenience also plays a part. Each kernel on an ear of our genetic corn represents an F2 offspring. This means students can immediately begin collecting data without performing genetic crosses themselves. Since there are generally 200 or more kernels per ear, it takes only a few ears to produce reliable data.
Corn kernels express numerous phenotypes that are easy to recognize. The phenotypes we typically use involve the color or shape of the kernel. Carolina maintains parental stocks of yellow and purple colors. We also keep parental stocks of starchy and sweet corn, which can be identified by shape. As an ear of sweet corn dries, it loses water and wrinkles. Starchy corn loses much less water as it dries, so the kernels remain plump. Using these parental stocks, we make 2 monohybrid crosses: purple crossed with yellow, and starchy crossed with sweet.
In the crosses we produce, the first phenotype is due to a dominant allele and the second is due to a recessive allele of the same gene. Thus, the F1 of the purple:yellow cross expresses the purple phenotype but carries the recessive allele for yellow, and so on. When the F1 kernels are planted and allowed to freely cross-pollinate, the recessive phenotype reappears in the resulting F2 ears in a 3:1 ratio. For example, the breakdown for the purple:yellow cross consists of 3 purple (dominant) and 1 yellow (recessive). The same 3:1 ratio is also obtained for the F2 of the starchy:sweet cross.
| Purple:Yellow Starchy
(F2 3:1 Ratio)
Middle school or high school biology classes can explore introductory genetics with our Monohybrid Genetics with Corn Kit. A beginning-level kit, it’s easy to perform and requires only a basic knowledge of genetics. The activity featured in the student guide uses corn ears that result from a purple:yellow cross or a starchy:sweet cross. The contrasting sets of phenotypes are easy to distinguish, even for beginning students, and little time is needed to prepare the lab. Minimal prep time, reusable, inexpensive, and effective—good reasons to try corny genetics in your classroom.