Phenotypic Ratios of Corn Experiment
Monohybrid and Dihybrid Crosses Experiment

Tips for Phenotypic Ratios Science Fair Projects

When you are working on collecting visual data or descriptive data it is important that you organize all of the information that you collect. Spreadsheets work great for this process. They not only will help you to keep your data organized, but they will also automate your analysis processes.

Objectives:

To calculate the phenotypic ratios for some monohybrid and dihybrid crosses. To determine the genotypes of parents from the phenotypic ratios of their offspring.

Materials needed:

mutant corn ears
pencil and paper
straight pins
calculators

Background:

Commercially available corn represent crosses between various parental genotypes. Results of a cross between pure-breeding purple kernel corn and pure-breeding yellow kernel corn produces offspring which are all purple (demonstrating dominance). A cross between two of these offspring produce 3/4 purple and 1/4 yellow kernel corn. These are the commercially available ears.

Strategy:

Obtain ears of corn representing offspring of crosses from various mutant and wild type plants from a biological supply company. Divide the class into groups of two or three. Give each group an ear of corn. Place a pin at one end of a row of kernels to mark your starting row. Using a pencil to point to the kernels, one partner should indicate the phenotype of each kernel while the other partner keeps a tally.

Each ear of corn is labeled with a code.

Conclusions:

1. For each ear of corn, calculate and record the ratio of the phenotypes. Divide the number of purple by the number of yellow. Also, divide the number of starchy by the number of sweet.
2. From the data, determine the genotypes of the parents in each cross.
3. How do the actual offspring phenotype ratios compare with the expected ratios?