1. How can a genetic mutation be harmful in one environment and helpful in another? 2. Why do you think certain mutations persist if they can be lethal?
3. Why are there more people with sickle cell disease in one part of the world than in other parts?

your answer is "the 1950's"

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

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