This worksheet was created during the Covid-19 pandemic to be administered remotely on google classroom. You can download a google doc version and share it to students via Google classroom. Even though it was designed for remote learning, I plan to use this as a class case-study in future years because it so elegantly combines so many concepts related to genetics and evolution.
The activity was s adapted from Understanding Evolution: evolution.berkeley.edu which outlines mechanisms for how snakes evolved from lizards. The concept of enhancers is addressed, to explain how regulatory genes may have been mutated so that that genes that coded for limb expression did not turn on. The gene itself remains intact and plays a role in the development of legs and the penis. If students were in my classroom, I would have a very lively discussion about snake reproduction here.
Students learn that the Tbx4 gene is responsible for the hind limb development of chameleons and that gene is also active in ball pythons, which express tiny hind limbs. This gene is deactivated in most snakes, like the boa constrictor, which does not have tiny hind limbs. Though the story does not
Students also analyze how this limb enhancer might be expressed differently in different organisms and its relationship to the development of a penis. Finally, students compare the evolution of snakes to that of whales, who also lost their hind limbs during the course of evolution.
To access the google doc, click the download button below and choose “make a copy” so that a version gets placed on your own drive. This will allow you to edit and share with students.
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HS-LS4-1 Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence