how many plants are dihybrid in F2 generation of dihybrid cross

Firstly dihybrid cross shows the possible recombination in gametes.

In dihybrid cross you will get 4 types of phenotypes and their ratio will be 9:3:3:1 (3:1 *3:1) and you will get 16 possible gametes after recombination,and they will be in the ratio 1:2:1:2:4:2:1:2:1 (1:2:1 *1:2:1).

DIHYBRID CROSS -DEFINITION

A cross made to study the inheritance of two characters or two pairs of contrasting forms or two pairs of different alleles is known as dihybrid cross. 
Example: 
Crossing of pure yellow, Round seeded plant with green, Wrinkled seeded pisum plants 
Character -1 - seed colour Yellow --- green 
Character - 2 - seed shape Round -----wrinkled

2. PHENOTYPIC HYPOTHESIS OF DIHYBRID CROSS

A. Crossing of ‘p’ generation:
Mendel crossed pure yellow, round seeded plant with pure green wrinkled

seeded plant. He got all yellow,Round seeded plants in ‘F1’ generation. These are dihybrids. 
The, ‘F1’ generation showed that yellow is dominant over green and round is dominant over wrinkled forms. This dominance was allready observed in monohybrid crosses. 
B. Crossing of ‘F1’ individuals:
Mendel allowed ‘F1’ di hybrid yellow, round seeded plants for self pollination. He got different types of individuals in ‘F2’.They are, 
1. Yellow, Round (Double dominant) 
2. Yellow,Wrinkled (Recombinant-I) 
3. Green, Round (Recombinant-Il) 
4. Green, Wrinkled (Double recessive) 
The above ‘4’ types of inidividuals are in the ratio of 9/1 6: 3/16: 3/16: 1/16 respectively. 
‘F2’ ‘dihybrid ratio led mendel to propose the law of independent assortment.

3. GENE HYPOTHESIS OF DIHYBRID CROSS

The yellow colour controlling gene is represented as ‘Y’ . The green colour controlling gene is represented as ‘y’. The round shape controlling gene is represented as ‘R’. The wrinkled shape controlling gene is represented as ‘r’. 
A. Genotypes of ‘P’generation: 
The genotype of pure yellow round seeded plant is ‘YY RR’. The genotype of double recessive green wrinkled seeded plant is ‘yy rr’

B. Crossing of pure ‘P’-.generation:

Pure yellow round seeded plant (YY RR) produced only one type of gametes (YR) type. All gametes carried ‘Y’ and ‘ R’ genes to the F1 generation. Pure green wrinkled seeded plant (yy rr) also produced one type of gametes (yr). When ‘YR’ type of gametes were fertilized by ‘yr’ type of gametes, all F1 inidividuals produced were dihybrid yellow round seeded plants(YyRr). The F1 generation indicates that yellow colour (Y) and round shape (R) controlling genes are dominant over green colour (y) and wrinkled shape (r) controlling genes respectively like in monohybrid crosses.

C. Crossing of’F1’dyhibrid individuals:

Mendel allowed self pollination in dihybrid yellow round seeded plants (YyRr). The ‘F1’ female produced ‘4’ types of ova. They. are YR, Yr, yR and yr. Like wise male also produced ‘4’types of pollen grains. They are YR, Yr, yR, and yr. When the above ‘4” types of ova were fertilized by the above ‘4’ types of pollen grains, Mendel got ‘4’ different phenotypes and ‘9’ different genotypes in F2 generation. 
The ‘F2’generation is represented in punnet’s squares or checker board.

4. ‘F2’ – PHENOTYPIC RATIO

In ‘f2’ generation, two parent phenotypes and two recombinats are 
produced. They are, 
I. Double dominant (VeIIow,Round) -- 9/16. 
ii. Recombinant - I (Yellow, Wrinkled ) --- 3/16. 
iii. Recombinant -Il (Green, Round) --- 3/16. 
iv. Double rcessive (Green, Wrinkled) --- 1/16. 
In ‘F2’ generation, if we observe the phenotypic ratio of one character that is either the ratio of yellow and green or Round and Wrinkled, it is 12/16: 4/16 or 3:1 . So, in dihybrid cross, the phenotypic ratio of one character is not effected by phenotypic ratio of another.

5. ‘F2’ - GENOTYPIC RATIO

In F2 generation the ‘1 6’ individuals of 4 different phenotypes contain ‘9’ different genotypes.

Total 16 plants.
Mendel observed that the F2 progeny of his dihybrid cross had a 9:3:3:1 ratio and
produced nine plants with round, yellow seeds, three plants with round, green seeds, three plants with wrinkled, yellow seeds and one plant with wrinkled, green seeds.

9;3;3;1