In a plant, tallness is dominant over dwarfness and red flower is dominant over white. Starting with the parents, work out a dihybrid cross. What is the standard dihybrid ratio? Do you think the values would deviate if the two genes in question are interacting with each other?

(D) The parents are $TTRR$ (Tall Red) and $ttrr$ (Dwarf White).
$F_{1}$ generation: $TtRr$ (Tall Red) $\times$ $TtRr$ (Selfing).
$F_{2}$ generation Punnett Square:

Gametes	$TR$	$Tr$	$tR$	$tr$
$TR$	$TTRR$ (Tall Red)	$TTRr$ (Tall Red)	$TtRR$ (Tall Red)	$TtRr$ (Tall Red)
$Tr$	$TTRr$ (Tall Red)	$Ttrr$ (Tall White)	$TtRr$ (Tall Red)	$Ttrr$ (Tall White)
$tR$	$TtRR$ (Tall Red)	$TtRr$ (Tall Red)	$ttRR$ (Dwarf Red)	$ttRr$ (Dwarf Red)
$tr$	$TtRr$ (Tall Red)	$Ttrr$ (Tall White)	$ttRr$ (Dwarf Red)	$ttrr$ (Dwarf White)

The standard dihybrid phenotypic ratio is $9:3:3:1$.
Yes, the values would deviate if the two genes interact with each other (e.g., epistasis or complementary gene action), as the independent assortment of traits would be altered.