A dihybrid cross is a cross involving two traits. For example, seed shape and seed colour.
A cross between a plant with round, yellow seed (true breed) and a plant with wrinkled, green seed (true breed)
=> Round is dominant whereas wrinkled is recessive
=> Yellow is dominant whereas green is recessive
=> R - round, r - wrinkled, Y - yellow, y - green
=> F2 ratio is 9 : 3 : 3 : 1
Parent phenotypes: Round, yellow X Wrinkled, green
Parent genotypes: RRYY X rryy
Gametes: RY RY ry ry
F1 genotypes: RrYy RrYy RrYy RrYy
F1 phenotypes: Round, Round, Round, Round,
yellow yellow yellow yellow
F1 self-crossed
F1 phenotypes: Round, yellow X Round, yellow
F1 genotypes: RrYy X RrYy
Gametes: RY Ry rY ry RY Ry rY ry
F2 genotypes and phenotypes:
RRYY (Round, yellow)
RRYy (Round, yellow)
RrYY (Round, yellow)
RrYy (Round, yellow)
RRYy (Round, yellow)
RRyy (Round, green)
RrYy (Round, yellow)
Rryy (Round, green)
RrYY (Round, yellow)
RrYy (Round, yellow)
rrYY (Wrinkled, yellow)
rrYy (Wrinkled, yellow)
RrYy (Round, yellow)
Rryy (Round, green)
rrYy (Wrinkled, yellow)
rryy (Wrinkled, green)
F2 ratio: 9 (Round, yellow) : 3 (Round, green) : 3 (Wrinkled, yellow) : 1 (Wrinkled, green)