Which is a clue that a chemical change has occured?
a. a beaker suddenly becomes very warm when you mix two room-temperature liquids in it.
b. a liquid forms bubbles when it reaches a high temperature.
c. water changes color when you add food coloring to it.
d. a car door feels hot if you touch it on a summer afternoon.

4. multiple crosses were made between true-breeding lines of black and yellow labrador retrievers. all the f1 progeny were black. when these progeny were intercrossed, they produced an f2 consisting of 91 black, 39 yellow and 30 chocolate. a. propose an explanation for the inheritance of coat color in labradors. b. propose a biochemical pathway for coat color determination and indicate how the relevant genes control coat coloration.