In the mythical beast Nechnüm nreyab, horn length is an example of continuous variation, under the control of five genes: A, B, C, D, and E. Each of these genes segregates an additive and a non-additive allele. Horn length can be: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 or 22 centimeters long.
a. How many different genotypes encode 20-cm horns? List them all.
b. Consider a cross between AaBBCcddEe and AabbCCDdee individuals. What is the shortest horn possible in the offspring of this cross?