EVO FINAL EXAM.docx - The Stickleback Fish A Story of...

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The Stickleback Fish - A Story of Modern Evolution This activity uses a virtual lab created by HHMI Biointeractive . To complete this activity students will need a computer with an internet connection and headphones to access videos. This worksheet is modified from the student worksheet provided by HHMI. Also, make sure that your browser allows pop-up windows. Background Infomation Go to: biol.co/stickfish-bg and read the background information about the stickleback fish. 1. Summarize what happened to the fish in Loberg Lake, include an explanation for WHY it happened. After the end of the last ice age 10,000 years ago, populations of marine stickleback fish became stranded in freshwater lakes dotted throughout the Northern Hemisphere in places like Alaska and British Columbia. These fish have adapted to a freshwater environment drastically different than the ocean. Stickleback bodies have undergone a dramatic transformation, some populations completely losing long projecting body spines that defend them from large predators. Various scientists, including David Kingsley and Michael Bell, have studied living populations of three spine sticklebacks, identified key genes and genetic switches in the evolution of body transformation, and even documented the evolutionary change over thousands of years by studying a remarkable fossil record from the site of an ancient lake ten million years ago. The Ectodysplasin gene appears to be responsible for changes in body armor in many freshwater stickleback populations. Recessive low-armored gene variations are found in about 1% of marine sticklebacks. Evidence suggests that it is this variant that is repeatedly being selected for in freshwater environments. Introduction: 2. Define "model organism." Model organisms are the species particularly nonhuman that are extensively studied to understand certain biological phenomena. 3. What is the purpose of the spines? Spines protect ocean stickleback fish when they are threatened they can simultaneously flare out their pair of pelvic spines and three dorsal spines, making it difficult for predators to swallow them. The back spines stick up and the pelvic spine out at almost a perpendicular angle, making it hard for a predatory fish that catches a stickleback to swallow it.
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4. How did ancestral populations of ocean-dwelling fish come to live in freshwater lakes? Ocean-dwelling fish come to live in freshwater lakes at the end of the last ice age. Lakes formed as the glaciers melted and these lakes provided new breeding grounds for stickleback swimming to these lakes from the ocean. The connections between some of the lakes and the ocean were cut off as ice continuously to melt causing the land to become elevated. The researchers conclude that the stickleback populations became trapped in these lakes and adapted to living exclusively in fresh water.
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