Question

A tall pea plant bearing violet flowers is given with its unknown genotypes. Explain by working out the crosses how would you find the correct genotypes with respect to the two traits mentioned only by 'selfing' the given plants.

Answer 1

Tall plant = TT/Tt

Violet flowers = WW/Ww

Genotype of given plant could be either of the assumed four: TTWW, TTWw, TtWW, TtWw

Case 1

Selfing of TTWW

	TW
TW	TTWW

All tall and violet, then genotype of parent is TTWW.

Case 2

Selfing of TTWw:

	TW	Tw
TW	TTWW	TTWw
Tw	TTWw	TTww

Phenotypic ratio: 3 : 1 (3 tall violet : 1 tall white) then Parent is TTWw.

Case 3

Selfing of TtWW

	TW	tW
TW	TTWW	TtWW
tW	TtWW	ttWW

Phenotypic ratio 3 : 1, (3 tall violet : 1 dwarf violet) then Parent is TtWW

Case 4

Selfing of TtWw:

	TW	Tw	tW	tw
TW	TTWW	TTWw	TtWW	TtWw
Tw	TTWw	TTww	TtWw	Ttww
tW	TtWW	TtWw	ttww	ttWw
Tw	TtWw	Ttww	ttWw	ttww

If phenotypic ratio 9 : 3 : 3 : 1, then parent is TtWw.