Question

Pure-tall (TT) pea plants are crossed with pure-dwarf (tt) pea plants. The pea plants obtained in F1 generation are then self-pollinated to produce F2 generation. 
(i) What do the plants of F1 generation look like? Justify your answer. 
(ii) What is the ratio of pure-tall plants to pure-dwarf plants in F2 generation?

Hint:

In the F2 generation, a 3:1 phenotypic ratio is observed when crossing two heterozygous plants (Tt).

Answer 1

(i) All plants in the F1 generation will be heterozygous (Tt) and tall because tall (T) is dominant over dwarf (t). Consequently, all F1 plants will display the tall phenotype.
(ii) The F2 generation results from self-pollination of the F1 plants (Tt). This will produce offspring with a 3:1 phenotypic ratio: three tall plants for every one dwarf plant: \[ {Phenotypic ratio:} \ 3 \ {tall}: 1 \ {dwarf} \] 
Therefore, in the F2 generation, the ratio of pure-tall plants (TT) to pure-dwarf plants (tt) is 1:3.