Using the established rules of Mendel and others, predicting the outcome of genetic crosses in model organisms is a common exercise for college students. Frequently, one uses visible phenotypic markers such as curly wings, eye color, and abnormal bristles to identify genetic outcomes. Yet many genetically-based traits, such as behavioral and physiological characteristics, are not easily observed. To demonstrate that such traits can likewise display classical genetic inheritance, we utilized an optogenetic system in Drosophila to modify response to light. We utilized the inheritance of behavioral responses associated with light-activated channelrhodopsin in motor neurons and body wall muscles. The frequency of responsive animals was quantified over multiple generations beginning with two pure-breeding (homozygous) strains, each containing one of the two components needed to produce the light-sensitive proteins. The use of light-sensitive channels to examine the predicted genetic outcomes is an approach which can be used in teaching classical genetic principles using non-traditional phenotypes. Green fluorescent protein (GFP) can be expressed to illustrate which cells are expressing channel rhodopsin. This introduces concepts of transgenesis, genetically-modified organisms, and genetic contributions to behavior. In addition to basic dominant and recessive allelic relationships, the experiments introduce more complex genetic concepts, such as epistasis, gene expression and cellular diversity, as well as physiological and behavioral traits of animals. This module is presented in a variety of ways depending on equipment availability and can be used in a hybrid or remote format with data provided.
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