Mendelian Genetics Lab
In this lab you'll use a test system of corn cobs and a couple of specific tools - the Punnett square and the chi-squared statistical test - to practice making hypotheses and predictions, and to analyze results in order to determine if the results of an experiment match your predictions, and in turn whether the results support your hypotheses.
Good hypotheses generate testable predictions; that is, you should be able to use a hypothesis to predict the results you will observe in a particular experiment if the hypothesis is correct. In order for a prediction to be testable, it must be expressed in terms of observable results.
How do you get from hypothesis to testable prediction? In this week's lab, you will be using the Punnett square as a tool that allows you to use a hypothesis about inheritance (for example, "trait X is dominant over trait Y", or "the parents of this group of offspring had the genotypes Bb and bb") to generate a testable prediction about phenotypic ratios in the offspring of a particular cross.
It is often helpful to remember the logical relationships between hypothesis, experiment, and prediction as an if/and/then statement:
IF the hypothesis is correct, AND a specific experiment is performed, THEN a specific result should be observed from the experiment.
After completing this activity and the relevant readings from the textbook, you should be able to:
- Explain the difference between phenotype and genotype.
- Use the hypothesis-experiment-prediction (if/and/then) model and the Punnett square diagramming technique to write hypotheses and to generate predictions of phenotypic ratios in the offspring of one-gene and two-gene breeding experiments (crosses).
- Use these predicted ratios to generate expected numbers of offspring showing each phenotype, and compare the expected numbers with the observed numbers of offspring of each phenotype using the chi-squared statistical test.
- Interpret the results of the chi-squared test to determine whether or not your hypothesis should be rejected.
Image Credits
Germplasm Enhancement for Maize (GEM) project By Keith Weller, USDA [Public domain], via Wikimedia Commons