Question

A tall pea plant bearing violet flowers with unknown genotype is given. Find the genotype by working out different crosses only by selfing the plants. Write the genotypic and phenotypic ratios of each cross shown by you.

Answer 1

Tall plant = TT/Tt

Violet flowers = WW/Ww

The genotype of the given plant could be any of the assumed four: TTWW, TTWw, TtWW, TtWw.

Case 1:

Selfing of TTWW → Gametes TW

All tall and violet, then genotype of parent is TTWW

Case 2:

Selfing of TTWw → Gametes TW, Tw

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

Case 3:

Selfing of TtWW → Gametes TW, tW

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

Case 4:

Selfing of TtWw → Gametes TW, Tw, tW, tw

Tall violet = 9
Tall white = 3
Dwarf violet = 3
Dwarf white = 1
If phenotypic ratio is 9 : 3 : 3 : 1, then parent is TtWw