The following coat colors are known to be determined by alleles at one locus in horses:
palomino = golden coat with lighter mane and tail
cremello = almost white
chestnut = brown
The following table gives ratios obtained in matings of the above varieties: $\begin{array} { l l l } Cross&Parents&Offspring\\1 & \text { cremello } \times \text { cremello } & \text { all cremello } \\ 2 & \text { chestnut } \times \text { chestnut } & \text { all chestnut } \\ 3 & \text { cremello } \times \text { chestnut } & \text { all palomino } \\ 4 & \text { palomino } \times \text { palomino } & 1 / 4 = \text { chestnut } \\ & & 1 / 2 = \text { palomino } \\ && 1 / 4 = \text { cremello } \end{array}$ a) Assign gene symbols for the genetic control of coat color on the basis of these data.
b) Diagram the last two matings.