Multiple cross 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 colour Labrador retrievers.
(b) Propose a biochemical pathway for a coat colour determination and indicate how the relevant genes control coat colouration.