I have used maize in a couple of ways in my teaching at St. Mary's College, and I would like to share this with others. I teach the introductory genetics course to biology majors which are comprised of mostly sophomores. I have used maize materials in two of my laboratory activities. These activities may be appropriate for an upper level high school genetics course as well.
In the initial lab of the course, I use sugary vs. normal kernels as a 3:1 demonstration and a review of goodness of fit tests. Then I assign exercises for their analysis and lab reports that include the following:
(1) Ears depicting a 9:3:3:1 ratio with sugary vs. normal and colored vs. colorless. Students are asked to test the data for independent assortment and to subdivide Chi square if appropriate.
(2) Seedlings that are the result of F2 selfs of plants heterozygous for two different virescent mutations (usually v4 and v17) are available in flats. Expectations are a 9:7 ratio. Students are asked to calculate the ratio, use goodness of fit tests, and deduce a feasible mode of inheritance and parental genotypes. It is a neat test in which to determine whether students can discern between a 1:1 ratio and a 9:7 ratio.
(3) Students also plant kernels in pots that test a backcross involving sugary1, lazy, and striate1. I obtain the seed by making backcrosses of Su/su La/la Sr/sr x su/su la/la sr/sr during the summer months. Using these ears, students remove all the kernels from two or more rows on the ear and plant the sugary and normal kernels in a separate series of pots. After they germinate into small seedlings, they place the pots on their sides in a horizontal position at the edge of a greenhouse bench. In a short time, normal and lazy seedlings can be discerned. Seedlings can now be scored for all three traits. This exercise is then a three-point test for the students to analyze, with sugary1 and lazy being linked and striate1 being independent of the other two traits.
In another exercise, maize microsporocytes are used to study the cytological aspects of meiosis. Students make their own preparations with propionic carmine staining procedures. All meiotic stages are identified as a class effort. A video system attached to a research-grade microscope is used to display and discuss the good preparations. Heterozygous translocations are sometimes inserted into the students' material to check their observation abilities. Their discovery of rings leads to pairing discussions.
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