Peanuts have two types of growth behavior: runner, which grows low to the ground, and bunch, which grows upright and branched. A true- breeding line of runner peanuts is crossed to a true breeding line of bunch peanuts. All of the F1 progeny grow as runners, so runners appears to be dominant. These F1 runner peanuts are then crossed to true breeding bunch peanuts (not a self cross) and the progeny show both phenotypes in a ratio of 3 bunch: 1 runner. Clearly one gene cannot explain this. How many genes are involved in the growth behavior phenotype, and was must the genotypes in the cross be? Assume recessive loss- of function mutations are involved.