A homozygous dominant tall pea plant bearing red flowers (TTRR) is crossed with a homozygous recessive dwarf pea plant bearing white flowers (ttrr).
Mention the phenotypic ratio of the F2 generation.
Topic: Dihybrid F2 phenotypic ratio
Answer
9 : 3 : 3 : 1
9 Tall with red flowers 3 Tall with white flowers 3 Dwarf with red flowers 1 Dwarf with white flowers
9:3:3:1 is the standard DIHYBRID ratio. Write out WHAT each number refers to, since the question asks for the PHENOTYPIC ratio and the phenotypes are the answer.
The order is always: both dominant (9), first dominant with second recessive (3), first recessive with second dominant (3), both recessive (1).
NOTE THE TWO NEW COMBINATIONS — tall with WHITE, and dwarf with RED. Neither appeared in the parents, and their appearance is the proof of INDEPENDENT ASSORTMENT: height and flower colour were inherited independently of each other.
Compare the MONOHYBRID ratio 3:1, which applies when only one character is followed.