digraph G {
size="10,10";  ratio = fill;
node [shape=square,width=1.5];
Genotype -> TraitA_T1;
Genotype -> TraitA_T2;
Genotype -> TraitA_T3;
Genotype -> TraitB_T2;
TraitA_T1 -> TraitB_T2;
TraitA_T1 -> TraitC_T3;
TraitB_T2 -> TraitC_T3;
}