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The discovery of gene switches in maize
Maize is introduced as a source of genetic variation. In the wild it is a red colour. The yellow colour of maize we normally see is a result of mutation and selective breeding. From 1945, geneticist Barbara McClintock grew maize plants in which the red colour reappeared. She cross pollinated specific plants, recording the parents and then the ratios of coloured to yellow kernels in the resulting cobs of corn. Her results did not match the expected ratios according to Mendelian principles. After 3 years of collecting data, McClintock worked out that genes were part of a dynamic system, and that genes were operated by gene switches.
Use as an introduction to the principles of plant breeding experiments and the importance of collecting enough data to ensure reliability. This can introduce the principles of gene interactions and gene switching. Follow up with practical work involving the counting of kernels on wild type corn cobs which are available from scientific suppliers. The students can then work on the genetic crosses involved and the phenotypic ratios produced. WARNING: The presenter uses a rifle to recreate scenes of shooting crows to protect crops.
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