(i) Characters are controlled by genes.
(ii) Each gene controls one character
(iii) There may be two or more forms of the gene
(iv) One form may be dominant over the other
(v) Genes are present on chromosomes
(vi) An individual has two forms of the gene whether similar or dissimilar
(vii) The two forms separate at the time of gamete formation
(viii) The two forms are brought together in the zygote. 

• RRYY x RRYY (round yellow x round yellow)
  
  Ans: Round yellow (RRYY)
• RrYy x RrYy (round yellow x round yellow)
  
  Ans: Round yellow (RRYY), Round yellow (RrYy), Round green (RRyy), Round green (Rryy), wrinkled yellow (rrYY), wrinkled yellow (rrYy), wrinkled green (rryy).
• rryy x rryy (wrinkled green x wrinkled green)
  
  Ans: wrinkled green (rryy)
• RRYY x rryy (round yellow x wrinkled green)
  
  Ans: Round yellow (RrYy)

• Parents	RRYY	rryy
  	round yellow	wrinkled green
  	RrYy (round yellow)	?

  Answer: RrYy (round yellow)

• Answer: Round yellow (RRYY), Round yellow (RrYy), Round green (RRyy), Round green (Rryy), wrinkled yellow (rrYY), wrinkled yellow (rrYy), wrinkled green (rryy). This can be shown by following Punette Square:

During Mendel’s experiment with dihybrid cross, it was seen that all the plants in F1 generation produced round and yellow seeds. However, in F2 generation, phenotypes of different seeds were different. This shows new combination of characters in F2 generation.

Out of round and wrinkled texture, round texture is the dominant character. Similarly, out of yellow and green colours, yellow colour is the dominant character. In F1 generation, all the plants produced round yellow seeds because of dominance of characters. But genotype of all plants was of mixed characters, i.e. RrYy. This happened because of Law of Independent Assortment. The gene for seed texture behaved independently of the gene for seed colour.

Due to this, the F2 generation showed different combination of genotype, viz. RRYY, RRYy, RrYY, RrYy, rrYY, rrYy, rryy. This can be shown by following punette square: