The Following Coat Colors Are Known to Be Determined by Alleles

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:
$\begin{array}{lll} \text { Cross } & \text { Parents } & \text { Offspring } \\\hline\\1 & \text { cremello } \times \text { cremello } & \text { all cremello } \\2 & \text { chestnut } \times \text { chestnut } & \text { all chestnut } \\3 & \text { cremello } \times \text { chestnut } & \text { all palomino } \\4 & \text { palomino } \times \text { palomino } & 1 / 4=\text { chestnut } \\& & 1 / 2=\text { palomino }\end{array}$ a) Assign gene symbols for the genetic control of coat color on the basis of these data.
b) Diagram the last two matings.