In peas,tallness is dominant over dwarfness and red colour of flowers is dominant over the white colour. When a tall plant bearing red flowers was pollinated with a dwarf plant bearing white flowers,the different phenotypic groups were obtained in the progeny in numbers mentioned against them:
Tall,Red $= 138$
Tall,White $= 132$
Dwarf,Red $= 136$
Dwarf,White $= 128$
Mention the genotypes of the two parents and of the four offspring types.

(A) The result shows that the four types of offspring are in a ratio of $1:1:1:1$. Such a result is observed in a test-cross progeny of a dihybrid cross. The cross can be represented as:
Parents: Tall and Red $(TtRr)$ $\times$ Dwarf and White $(ttrr)$
The gametes produced by the tall red parent $(TtRr)$ are $TR, Tr, tR, tr$,while the dwarf white parent $(ttrr)$ produces only $tr$ gametes.
The resulting offspring genotypes are:
$1. TtRr$ (Tall,Red)
$2. Ttrr$ (Tall,White)
$3. ttRr$ (Dwarf,Red)
$4. ttrr$ (Dwarf,White)
Thus,the genotypes of the parents are $TtRr$ and $ttrr$,and the genotypes of the four offspring types are $TtRr, Ttrr, ttRr,$ and $ttrr$.