It is a cross which involves two characters and two gene pair. it leads to dihybrid F₁ offspring.
Mendel worked with and crossed pea plants that differed in two characters, as is seen in the cross between a pea plant that has seeds with yellow colour and round shape, one that had seeds of green colour and wrinkled shape.
Mendel found that the seeds resulting from the crossing of the parents, had yellow coloured and round shaped seeds.
Thus, yellow colour was dominant over green colour and round shaped dominant over wrinkled.
Let us use the genotype symbol Y for dominant yellow seed and y for recessive green seed colour, R for round shaped seeds and r for wrinkled seed shaped.The genotype of the parents can then be written as RRYY and rryy.
The cross between the two plants can be written down.
The gametes RY and ry unite on fertilisation to produce the F₁ hybrid RrYy. When Mendel self hybridised the F₁ plants he found that 3/4th of F₂ plants had yellow seeds and 1/4th had green.
The yellow and green colour segregated in 3 : 1 ratio. Round and wrinkled seed shape also segregated in a 3 : 1 ratio. Just like in a Monohybrid cross .