Corn genetics - so many baby corns!
As a preview to the future unit on plant reproduction, note that corn make two distint types of flowers - one male (seen by the tassels) and one female (seen by the silks). An ear of corn is actually a collection of over a hundred offspring, neatly packaged onto a cob, able to be stored long term, perfect for studying genetics. Each corn kernel (seed) has a dormant embryo and an enhanced nutritive layer known as the endosperm, which will support the growing embryo until it germinates and can begin providing for itself via photosynthesis. (Seeds can also store fats/oils and proteins - think about the many different types of food products that come from these.)
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A few notes about corn phenotypes...
In the simplest terms, color in the corn kernel (specifically in the endosperm layer) is purple (dominant allele, P) in the wild type. Yellow corn is a mutant, albeit a more familiar form to most of us. Similarly, the shape of the kernel is familiar to us as a smooth rounded shape in sweet corn. But this is what is found in fresh corn. If it is dried the water in the sugar solution will evaporate and leave a small residue of sugar and a "shrunken" appearance. "Field corn," which is the predominant type of corn that you see growing along the highways, is not sweet, but starchy (containing at least one dominant Su allele). So when it dries, the (larger volume of) insoluble starch remains and the kernel is smooth. This field corn is destined to be consumed largely as animal feed, but also as raw material for biofuels, including fermentation processing. So, the corn that comes to mind for most of us - sweet corn - is a mutant two ways - homozygous recessive for both color (pp) and shape (susu)!
Lab Instructions:
- Collect data from the corn ears in class for each of these four categories: purple starchy, purple sugary, yellow starchy, yellow sugary.
- Pay attention to the effect of shriveling on the yellow color!
- You may need to create a category for uncertainties.
- Refer to the dihybrid cross Punnett Square on pea seed color and shape on the main genetics page.
- Once you have collect data, use the slides below to help work through the application of a standard statistical test for distribution, chi-square test.
REPORT CONCLUSION ONLY. Include:
- LIST OF STEPS TO TAKE TO MAKE DATA TABLE COMPLETE
- ANALYSIS OF DATA AND CONCLUSION TO BE DRAWN FROM THEM (FOLLOW THROUGH CHI-SQUARED TEST BELOW IF YOU ARE INTERESTED)
- EVALUATION OF THE EXPERIMENTAL DESIGN, DATA COLLECTED, INCLUDING MULTIPLE TYPES OF EXPERIMENTAL ERROR
- SUGGESTIONS FOR IMPROVEMENTS OF ALL TYPES (NOT JUST FOR HUMAN ERRORS)
Extension - Epigenetic Effects in Corn...where did the speckles come from??
