Multiple crosses were made between true-breeding lines of black and yellow Labrador retrievers. All F1 progeny were black. When this progeny were inter-crossed, they produced an F2 consisting of 91 black, 39 yellow, and 30 chocolate.

a) propose an explanation for the inheritance of coat color in Labrador retrievers.

b) Propose a biochemical pathway for coat color determination and indicate how the relevant genes control coat coloration.